Bug 416739 - Panel disappears from time to time and after a while re-appears
Summary: Panel disappears from time to time and after a while re-appears
Status: RESOLVED DUPLICATE of bug 427278
Alias: None
Product: plasmashell
Classification: Plasma
Component: Desktop Containment (show other bugs)
Version: 5.24.4
Platform: Gentoo Packages Linux
: NOR normal
Target Milestone: 1.0
Assignee: Marco Martin
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2020-01-25 11:31 UTC by Erik Quaeghebeur
Modified: 2022-05-18 11:17 UTC (History)
22 users (show)

See Also:
Latest Commit:
Version Fixed In:
Sentry Crash Report:


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Description Erik Quaeghebeur 2020-01-25 11:31:00 UTC
SUMMARY
Since about to weeks, my panel has started to disappear and then after a while re-appear. There is no clear indication of why it disappears or re-appears. Logging out and back in again doesn't fix it in general, but it may happen that the disappearing and reappearing occurs on logging in. But both have also happened while being logged in.

When I try to add a new panel (via right-click menu on desktop), it does not appear. But later, when the panel re-appears, that extra panel also appears.

As you can imagine, this is very annoying. I can imagine that the information I provide is insufficient to help me fix things. But I'm willing to test things, so please aid me in that.

STEPS TO REPRODUCE
Unknown.

OBSERVED RESULT
Panel disappearing.

EXPECTED RESULT
Panel stays put, as before.

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.17.4
KDE Frameworks Version: 5.64.0
Qt Version: 5.13.2
Comment 1 Nate Graham 2020-01-28 18:35:02 UTC
Yuck, that does sound very annoying. :/

Do you happen to be using multiple activities or screens?
Comment 2 Erik Quaeghebeur 2020-01-28 20:38:52 UTC
(In reply to Nate Graham from comment #1)
> Do you happen to be using multiple activities or screens?
I use an external screen when at home, but not in a multi-screen setup. So the external screen is the only one then active (and is primary).
Comment 3 Nate Graham 2020-01-28 21:15:24 UTC
Ah, so your primary screen changes frequently between a laptop's built-in display and an external screen? Am I understanding that right?
Comment 4 Erik Quaeghebeur 2020-01-28 21:19:33 UTC
(In reply to Nate Graham from comment #3)
> Ah, so your primary screen changes frequently between a laptop's built-in
> display and an external screen? Am I understanding that right?
Yes, but I did not experience the panel disappearances as being related to that. I will try to pay close attention to it next time it happens.
Comment 5 Nate Graham 2020-01-28 21:26:52 UTC
I suspect it's related, even if the effect is delayed.
Comment 6 Erik Quaeghebeur 2020-01-31 08:42:54 UTC
(In reply to Erik Quaeghebeur from comment #4)
> […] I will try to pay close attention to it next time it happens.
It happened again, now after a shutdown/start going from unconnected to docked, which probably support your suspicions.

Might there be a way to trigger reappearance of the panel, based on the assumption that it is related to screen switching?
Comment 7 Nate Graham 2020-01-31 19:22:41 UTC
Seems similar to Bug 356225, if not an outright duplicate.
Comment 8 Erik Quaeghebeur 2020-01-31 19:54:30 UTC
(In reply to Nate Graham from comment #7)
> Seems similar to Bug 356225, if not an outright duplicate.
Well, I just activated the laptop screen and didn't get the panel back. However, now my external screen's background has vanished. I can't even get a right-click menu anymore…
Comment 9 Kevin Kaland 2020-02-04 11:27:15 UTC
Hmm, it sounds plausible that this might be a duplicate in my case. I have my laptop screen set to black out when I connect my external monitor. Perhaps the Panel is on that screen even though it's disabled? I will try to enable it next time this happens and see if the panel is there.
Comment 10 Erik Quaeghebeur 2020-02-12 12:35:23 UTC
Still present in 5.17.5.
Comment 11 Kevin Kaland 2020-03-07 17:18:42 UTC
Still present in 5.18.2 on Manjaro (Arch Linux package).
Comment 12 Kevin Kaland 2020-04-21 11:51:49 UTC
Still in 5.18.4. I can also add that this seems to happen right after a KDE upgrade, either after the package including plasmashell (plasma-workspace on Manjaro, it appears).

I actually tried re-enabling the laptop monitor to see if the panel was there, but it was not. This was the output when I tried to `kstart5 plasmashell` on the CLI:


````
 ~  kstart5 plasmashell &                                                                                                                   1278ms  13:44:28
 %  ~  Omitting both --window and --windowclass arguments is not recommended                                                                        13:44:42
Icon theme "ubuntu-mono-dark" not found.
Icon theme "Mint-X" not found.
Icon theme "elementary" not found.
Job 1, 'kstart5 plasmashell &' has ended
         Icon theme "ubuntu-mono-dark" not found.                                                                                            13:44:42
Icon theme "Mint-X" not found.
Icon theme "elementary" not found.
````
Comment 13 Frederick Zhang 2020-04-26 09:54:50 UTC
I've also been experiencing this issue for a while now. I'm using a multi-head setup but I never connect/disconnect monitors and I've got a static xrandr script applied via SDDM DisplayCommand.

In my case it seems that plasma-org.kde.plasma.desktop-appletsrc is the only file that gets reset and usually what I need to do is simply restoring the correct file from a snapshot.
Comment 14 Thomas 2020-04-28 23:19:02 UTC
Hello,
same here. 
Laptop Lenovo T400 with external monitor
Kubuntu 20.04 (fresh install) 

After awaking from sleep mode the external monitor comes up with a wrong resolution. (This may be an other Issue)

I change it back to the correct resolution and after Apply that display appear with the correct resolution but without the panel. (Right click - add panel didn't help) 
 
Deleting the file "plasma-org.kde.plasma.desktop-appletsrc" and restart KDE brings the taskbar back.
Comment 15 Mika Norén 2020-04-29 14:48:54 UTC
I confirm this is still an issue with the latest Arch update as of this date.
All my computers that somehow involve more than one screen (laptops, desktop etc.) has this problem. It even happens when only one screen is enabled and the rest remains disabled either through the control center application, or via xrandr/xorg.conf.

Seems the plasma environment detects monitors as "new screens" every now and then for no apparent reason. This may or may not happen at cold boot, sleep, powersave or just simply triggered by a dpms event.
Comment 16 Thomas 2020-05-01 14:53:55 UTC
Operating System: Kubuntu 20.04
KDE Plasma Version: 5.18.4
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8
Kernel Version: 5.4.0-28-generic
OS Type: 64-bit

Again some Tests. 
It can be reproduced, Panel disappears after sleep (mostly), reboot (every time)and sometimes after new login.

External monitor attached and laptop monitor disabled.
Comment 17 Kevin Kaland 2020-05-02 14:44:36 UTC
Yes, laptop monitor disabled is also my scenario. Perhaps I should enable it and check if this happens like that.
Comment 18 Thomas 2020-05-10 22:18:51 UTC
It's happens also with laptop monitor enabled.
Comment 19 Mika Norén 2020-05-14 05:07:34 UTC
In my dual screen setup, a mysterious third output appears in .config/plasmashellrc under section [ScreenConnectors]

What it's supposed to look like in my case:
[ScreenConnectors]
0=DisplayPort-0
1=DisplayPort-1

What it looks like when this bug triggers:
[ScreenConnectors]
0=DisplayPort-0
1=:0.0
2=DisplayPort-1

Sometimes it also looks like this:
[ScreenConnectors]
0=DisplayPort-0
1=DisplayPort-1
2=:0.0

To restore the previous screen configuration, I remove the :0.0 -line from the section mentioned, and restore the order of the remaining valid outputs.
I save changes and restarts plasmashell. (killall plasmashell && plasmashell --replace)
Once plasmashell restarts, it's back to the intended screen configuration with all panels and widgets back in place again.

This might or might not happen at any time when screens are turned on after being off, computer restarts or resuming from sleep. It's random and there seem to be no rime or reason to it.
Comment 20 Erik Quaeghebeur 2020-05-14 12:30:11 UTC
(In reply to Mika Norén from comment #19)
> In my dual screen setup, a mysterious third output appears in
> .config/plasmashellrc under section [ScreenConnectors]
I looked at my .config/plasmashellrc while my laptop is disconnected from any external screen and there have

[ScreenConnectors]
0=LVDS1
2=LVDS-1-unknown
3=XWAYLAND1
4=:0.0
5=Screen30
6=HDMI1

This is on a laptop with 1 LVDS (internal), one VGA, and one DP connection. I have no idea what all entries except the first mean. Could I remove all those connections?
Comment 21 Mika Norén 2020-05-19 19:18:45 UTC
(In reply to Erik Quaeghebeur from comment #20)
> (In reply to Mika Norén from comment #19)
> > In my dual screen setup, a mysterious third output appears in
> > .config/plasmashellrc under section [ScreenConnectors]
> I looked at my .config/plasmashellrc while my laptop is disconnected from
> any external screen and there have
> 
> [ScreenConnectors]
> 0=LVDS1
> 2=LVDS-1-unknown
> 3=XWAYLAND1
> 4=:0.0
> 5=Screen30
> 6=HDMI1
> 
> This is on a laptop with 1 LVDS (internal), one VGA, and one DP connection.
> I have no idea what all entries except the first mean. Could I remove all
> those connections?

That's quite a bunch indeed.
Lemme make a guess:
  0=LVDS1            <-- Your LCD panel on the laptop itself
  2=LVDS-1-unknown   <-- Your LCD panel on the laptop itself seem to have been duble-detected an one point. Maybe remove.
  3=XWAYLAND1        <-- No idea. Some virtual display from Wayland?
  4=:0.0             <-- Usually this one is the mysterious entry that spooks around. I just delete it. It randomises itself from time to time. No idea why though.
  5=Screen30         <-- No idea. Another virtual display?
  6=HDMI1            <-- At some point you had an external display connected to your laptop. It has been registered and saved at position 6.

I guess you could reove everything but the ones you know you use. May I suggest trying this? (Save the old setup in case you need to refer to it again)

[ScreenConnectors]
0=LVDS1
1=HDMI1
Comment 22 Erik Quaeghebeur 2020-05-20 07:29:51 UTC
(In reply to Mika Norén from comment #21)
> I guess you could reove everything but the ones you know you use. May I
> suggest trying this?
I did. It doesn't help a bit… The same problem is still present, even with the right entries in this file.
Comment 23 tmdm 2020-05-26 16:40:53 UTC
Same problem. But the panel disappears only after a reboot. it helps, but only until reboot: kquitapp5 plasmashell && kstart5 plasmashell &. Second monitor through Display Port. Manjaro, KDE Plasma 5.18.5.
Comment 24 tmdm 2020-05-26 18:50:46 UTC
Sorry, connecting a second monitor through the VGA. If it is important.
Comment 25 wladypauly 2020-06-16 08:52:07 UTC
This bug also affects me, KDE Neon with all updates, Plasma 5.19.0, KDE Frameworks 5.71.0, Qt version 5.14.2. Laptop Lenovo Think Pad Edge E531 with external monitor connected through HDMI.
The panels  disappear after a reboot or after resuming from sleep. Removing the file  ~/.config/plasma-org.kde.plasma.desktop-appletrc and restarting plasmashell (with     kquitapp5 plasmashell && kstart5 plasmashell &) gives the following output
kquitapp5 plasmashell && kstart5 plasmashell & 
[1] 6293
 Edge-E531>>>11:44:44 Ma iun 16>>
~
>>>Omitting both --window and --windowclass arguments is not recommended
QML debugging is enabled. Only use this in a safe environment.
file:///usr/share/plasma/packages/org.kde.desktoptoolbox/contents/ui/ToolBoxButton.qml:217: TypeError: Cannot call method 'action' of null
file:///usr/share/plasma/packages/org.kde.desktoptoolbox/contents/ui/ToolBoxButton.qml:211: TypeError: Cannot call method 'globalAction' of null
file:///usr/share/plasma/packages/org.kde.desktoptoolbox/contents/ui/ToolBoxButton.qml:205: TypeError: Cannot call method 'action' of null
file:///usr/share/plasma/packages/org.kde.desktoptoolbox/contents/ui/ToolBoxButton.qml:33: TypeError: Cannot read property 'editMode' of null
file:///usr/share/plasma/packages/org.kde.desktoptoolbox/contents/ui/ToolBoxButton.qml:46: TypeError: Cannot read property 'editMode' of null
file:///usr/share/plasma/packages/org.kde.desktoptoolbox/contents/ui/ToolBoxButton.qml:47: TypeError: Cannot read property 'editMode' of null
trying to show an empty dialog
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:71: TypeError: Cannot read property 'pluginName' of null
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:73: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:74: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:75: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:76: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:32: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:33: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:34: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:35: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/packages/org.kde.paneltoolbox/contents/ui/main.qml:31: TypeError: Cannot read property 'formFactor' of null
file:///usr/share/plasma/packages/org.kde.paneltoolbox/contents/ui/main.qml:103: TypeError: Cannot read property 'editMode' of null
file:///usr/share/plasma/packages/org.kde.paneltoolbox/contents/ui/main.qml:48: TypeError: Cannot read property 'editMode' of null
file:///usr/share/plasma/packages/org.kde.paneltoolbox/contents/ui/main.qml:37: TypeError: Cannot read property 'editMode' of null
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:89:5: QML Binding: Not restoring previous value because restoreMode has not been set.
This behavior is deprecated.
You have to import QtQml 2.14 after any QtQuick imports and set
the restoreMode of the binding to fix this warning.
In Qt < 6.0 the default is Binding.RestoreBinding.
In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.

file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:89:5: QML Binding: Not restoring previous value because restoreMode has not been set.
This behavior is deprecated.
You have to import QtQml 2.14 after any QtQuick imports and set
the restoreMode of the binding to fix this warning.
In Qt < 6.0 the default is Binding.RestoreBinding.
In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.

file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:73:5: QML Binding: Not restoring previous value because restoreMode has not been set.
This behavior is deprecated.
You have to import QtQml 2.14 after any QtQuick imports and set
the restoreMode of the binding to fix this warning.
In Qt < 6.0 the default is Binding.RestoreBinding.
In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.

file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:73:5: QML Binding: Not restoring previous value because restoreMode has not been set.
This behavior is deprecated.
You have to import QtQml 2.14 after any QtQuick imports and set
the restoreMode of the binding to fix this warning.
In Qt < 6.0 the default is Binding.RestoreBinding.
In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.

QQmlExpression: Attempted to evaluate an expression in an invalid context
file:///usr/share/plasma/plasmoids/org.kde.plasma.kickoff/contents/ui/Kickoff.qml:36: TypeError: Cannot read property 'location' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.kickoff/contents/ui/Kickoff.qml:40: TypeError: Cannot read property 'formFactor' of null
org.kde.plasmaquick: Applet preload policy set to 1
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:76:9: Unable to assign [undefined] to QStringList
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:75:9: Unable to assign [undefined] to int
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:75:9: Unable to assign [undefined] to int
file:///usr/share/plasma/wallpapers/org.kde.image/contents/ui/main.qml:76:9: Unable to assign [undefined] to QStringList
trying to show an empty dialog
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Desktop.qml:146:19: QML Loader: Binding loop detected for property "height"
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Desktop.qml:146:19: QML Loader: Binding loop detected for property "height"
evaluating startup script: "/usr/share/plasma/shells/org.kde.plasma.desktop/contents/layout.js"
Activity added twice "c399ba26-23b3-4d2a-a647-d95cd961ded9"
qrc:/plasma/plasmoids/org.kde.plasma.volume/contents/ui/main.qml:41: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.devicenotifier/contents/ui/devicenotifier.qml:38: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.kdeconnect/contents/ui/main.qml:55: TypeError: Cannot read property 'formFactor' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.keyboardindicator/contents/ui/main.qml:32: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/main.qml:148: TypeError: Cannot read property 'nativeInterface' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.vault/contents/ui/main.qml:33: TypeError: Cannot read property 'nativeInterface' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.vault/contents/ui/main.qml:32: TypeError: Cannot read property 'nativeInterface' of null
qrc:/plasma/plasmoids/org.kde.plasma.networkmanagement/contents/ui/main.qml:82: TypeError: Cannot read property 'expanded' of null
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/applet/CompactApplet.qml:60: TypeError: Cannot read property 'Layout' of null
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/applet/CompactApplet.qml:78: TypeError: Cannot read property 'Layout' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:110: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:111: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:102: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:38: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/Tooltip.qml:83: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/Tooltip.qml:72: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/Tooltip.qml:98: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:77: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/Tooltip.qml:98: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:54: TypeError: Cannot read property 'compactRepresentationItem' of null
file:///usr/share/plasma/packages/org.kde.paneltoolbox/contents/ui/main.qml:31: TypeError: Cannot read property 'formFactor' of null
file:///usr/share/plasma/packages/org.kde.paneltoolbox/contents/ui/main.qml:103: TypeError: Cannot read property 'editMode' of null
file:///usr/share/plasma/packages/org.kde.paneltoolbox/contents/ui/main.qml:48: TypeError: Cannot read property 'editMode' of null
file:///usr/share/plasma/packages/org.kde.paneltoolbox/contents/ui/main.qml:37: TypeError: Cannot read property 'editMode' of null
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:89:5: QML Binding: Not restoring previous value because restoreMode has not been set.
This behavior is deprecated.
You have to import QtQml 2.14 after any QtQuick imports and set
the restoreMode of the binding to fix this warning.
In Qt < 6.0 the default is Binding.RestoreBinding.
In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.

file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:89:5: QML Binding: Not restoring previous value because restoreMode has not been set.
This behavior is deprecated.
You have to import QtQml 2.14 after any QtQuick imports and set
the restoreMode of the binding to fix this warning.
In Qt < 6.0 the default is Binding.RestoreBinding.
In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.

file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:73:5: QML Binding: Not restoring previous value because restoreMode has not been set.
This behavior is deprecated.
You have to import QtQml 2.14 after any QtQuick imports and set
the restoreMode of the binding to fix this warning.
In Qt < 6.0 the default is Binding.RestoreBinding.
In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.

file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:73:5: QML Binding: Not restoring previous value because restoreMode has not been set.
This behavior is deprecated.
You have to import QtQml 2.14 after any QtQuick imports and set
the restoreMode of the binding to fix this warning.
In Qt < 6.0 the default is Binding.RestoreBinding.
In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.

QQmlExpression: Attempted to evaluate an expression in an invalid context
file:///usr/share/plasma/plasmoids/org.kde.plasma.kickoff/contents/ui/Kickoff.qml:36: TypeError: Cannot read property 'location' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.kickoff/contents/ui/Kickoff.qml:40: TypeError: Cannot read property 'formFactor' of null
qrc:/plasma/plasmoids/org.kde.plasma.volume/contents/ui/main.qml:41: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.devicenotifier/contents/ui/devicenotifier.qml:38: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.kdeconnect/contents/ui/main.qml:55: TypeError: Cannot read property 'formFactor' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.keyboardindicator/contents/ui/main.qml:32: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/main.qml:148: TypeError: Cannot read property 'nativeInterface' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/global/Globals.qml:78:5: Unable to assign [undefined] to QObject*
file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/global/Globals.qml:138: TypeError: Cannot read property 'nativeInterface' of null
libkcups: Cancel-Subscription last error: 0 successful-ok
libkcups: Create-Printer-Subscriptions last error: 0 successful-ok
libkcups: Cancel-Subscription last error: 0 successful-ok
file:///usr/share/plasma/plasmoids/org.kde.plasma.vault/contents/ui/main.qml:33: TypeError: Cannot read property 'nativeInterface' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.vault/contents/ui/main.qml:32: TypeError: Cannot read property 'nativeInterface' of null
qrc:/plasma/plasmoids/org.kde.plasma.networkmanagement/contents/ui/main.qml:82: TypeError: Cannot read property 'expanded' of null
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/applet/CompactApplet.qml:60: TypeError: Cannot read property 'Layout' of null
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/applet/CompactApplet.qml:78: TypeError: Cannot read property 'Layout' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:110: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:111: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:102: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:38: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/Tooltip.qml:83: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/Tooltip.qml:72: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/Tooltip.qml:98: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:77: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/Tooltip.qml:98: TypeError: Cannot read property 'configuration' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/main.qml:54: TypeError: Cannot read property 'compactRepresentationItem' of null
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Desktop.qml:266: TypeError: Cannot read property 'longDuration' of null
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/styles/org.kde.desktop.plasma/Units.qml:94: TypeError: Cannot read property 'longDuration' of null
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/styles/org.kde.desktop.plasma/Units.qml:100: TypeError: Cannot read property 'shortDuration' of null
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/styles/org.kde.desktop.plasma/Units.qml:106: TypeError: Cannot read property 'veryLongDuration' of null
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:110: TypeError: Cannot read property 'iconSizes' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/global/Globals.qml:145: TypeError: Cannot read property 'gridUnit' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/global/Globals.qml:146: TypeError: Cannot read property 'largeSpacing' of null
file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/global/Globals.qml:149: TypeError: Cannot read property 'largeSpacing' of null
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Panel.qml:110: TypeError: Cannot read property 'iconSizes' of null
>>>Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
Plasma Shell startup completed
Both point size and pixel size set. Using pixel size.
Both point size and pixel size set. Using pixel size.
Both point size and pixel size set. Using pixel size.
trying to show an empty dialog
trying to show an empty dialog
file:///usr/share/plasma/plasmoids/org.kde.plasma.taskmanager/contents/ui/main.qml:100:5: QML TasksModel: Binding loop detected for property "groupingWindowTasksThreshold"
libkcups: CUPS-Get-Printers last error: 1030 No destinations added.
libkcups: Create-Printer-Subscriptions last error: 0 successful-ok
libkcups: Get-Jobs last error: 0 successful-ok
libkcups: Get-Jobs last error: 0 successful-ok
Both point size and pixel size set. Using pixel size.
libkcups: 0
libkcups: 0
KAStatsFavoritesModel::setFavorites is ignored
Entry is not valid "kontact.desktop" QSharedPointer(0x55f1b7f37540)
Entry is not valid "ktp-contactlist.desktop" QSharedPointer(0x55f1b7f37540)
Entry is not valid "kontact.desktop" QSharedPointer(0x55f1b7f37540)
Entry is not valid "ktp-contactlist.desktop" QSharedPointer(0x55f1b7f37540)
Entry is not valid "kontact.desktop" QSharedPointer(0x55f1b7fd3400)
Entry is not valid "ktp-contactlist.desktop" QSharedPointer(0x55f1b80dc860)
trying to show an empty dialog
Entry is not valid "kontact.desktop" QSharedPointer(0x55f1b8107d90)
Entry is not valid "ktp-contactlist.desktop" QSharedPointer(0x55f1b8107d90)
Entry is not valid "kontact.desktop" QSharedPointer(0x55f1b8107d90)
Entry is not valid "ktp-contactlist.desktop" QSharedPointer(0x55f1b8107d90)
file:///usr/share/plasma/plasmoids/org.kde.plasma.printmanager/contents/ui/PopupDialog.qml:102:13: QML PropertyChanges: Cannot assign to non-existent property "tooltipText"
Both point size and pixel size set. Using pixel size.
Both point size and pixel size set. Using pixel size.
Both point size and pixel size set. Using pixel size.
Both point size and pixel size set. Using pixel size.
Both point size and pixel size set. Using pixel size.
Both point size and pixel size set. Using pixel size.
Both point size and pixel size set. Using pixel size.
trying to show an empty dialog
Comment 26 Mika Norén 2020-06-25 18:08:32 UTC
(In reply to Erik Quaeghebeur from comment #22)
> (In reply to Mika Norén from comment #21)
> > I guess you could reove everything but the ones you know you use. May I
> > suggest trying this?
> I did. It doesn't help a bit… The same problem is still present, even with
> the right entries in this file.

I suspected so. 
Your setup is so messed up with different connections no wonder it doesn't work.

Then may I suggest delete/move the plasmashellrc file and start over. 
Then, once your configuration is done and supposed to be where it is, you take a backup of plasmashellrc file immediately. Once your problem reappears you compare the backup file with the current one with the invalid file. You should then spot what has gone wrong.
Comment 27 Thomas 2020-06-26 21:25:31 UTC
Status after some tests: 

ACTUAL system software:

Operating System: Kubuntu 20.04
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8
Kernel Version: 5.4.0-39-generic
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-3320M CPU @ 2.60GHz
Memory: 7,5 GiB of RAM



1 It appears after every reboot
2. Very usual setup - Laptop with an external monitor on VGA. Directly connected or via a docking station, doesn't matter 
3. Only few differences in the .desktop-appletsrc files.  

************ WORKING file (only the related entries) 

[Containments][10][Configuration]
PreloadWeight=10 

[Containments][2][Applets][6][Configuration]
PreloadWeight=100
SystrayContainmentId=7

[Containments][7][Applets][16][Configuration]
PreloadWeight=51 

[ScreenMapping]
itemsOnDisabledScreens=1,1,desktop:/moneyplex.desktop
screenMapping=desktop:/moneyplex.desktop,0,desktop:/FoxitReader.desktop,0  


************** BAD file after reboot with missing panel 

[Containments][10][Configuration]
PreloadWeight=0

[Containments][2][Applets][6][Configuration]
PreloadWeight=99
SystrayContainmentId=7

[Containments][7][Applets][16][Configuration]
PreloadWeight=56

[ScreenMapping]
itemsOnDisabledScreens=
screenMapping=desktop:/moneyplex.desktop,1,desktop:/FoxitReader.desktop,1


The PreloadWeight entries may be part of the problem.
Comment 28 s.v.savenko 2020-06-27 21:57:03 UTC
exactly same issue here
```
Operating System: Arch Linux
KDE Plasma Version: 5.19.2
KDE Frameworks Version: 5.71.0
Qt Version: 5.15.0
Kernel Version: 5.7.6-arch1-1
OS Type: 64-bit
```
Started after upgrade to 5.19.
Comment 29 s.v.savenko 2020-06-27 22:41:30 UTC
The difference between the working plasmashellrc and non-working one is
```working
[ScreenConnectors]
0=DP-1-1
```
```non-working
[ScreenConnectors]
0=DP-1-1
1=eDP-1-1
```
Only one monitor is active in both cases.
Comment 30 grego 2020-07-15 07:56:16 UTC
I started to experience exactly the same issue, hovewer, in my case I found a way to reproduce it. I commented on that already on Manjaro forum [1] so here's the copy of my findings:

>>>
I experienced the same issue today i.e. after a reboot my default panel has gone and I could not add it back nor any other panel via the context menu, the desktop wallpaper has reset to the default and my custom key bindings for the default panel have been gone equally.

I think I identified it to be related to my dual screen setup. My Lenovo L570 has a UHD 4K display connected via a mini-DP to DP cable. As I used to dual boot with Windows 10 I had the laptop lid open during boot and closed it when the login screen came on. This resulted in a cloned display on both the laptop and the 4K screen with the same low resolution of the laptop screen. After logging in the resolution gets adjusted to 4K and scaling of 150% is applied.

Today, however, I restarted from Windows 10 with the lid closed and the boot continued only on the 4K screen. When KDE login screen came up it was in the native 4K resolution without any scaling applied and after logging in my desktop was reset, the default panel gone etc. The same remained after logging out and in again, rebooting and even clearing cache, config files and applying other reset actions I was able to find. Resetting the theme to defaults helped bring the default panel back but it didn't persist the log out/in nor reboot cycle. Very frustrating.

Finally, I booted up with the laptop lid open and… bang! my panel was there back again. I repeated the same procedure a few times with the same result:

- **reboot with the lid open** and the laptop screen on during the boot and my **desktop and panels persist**
- **reboot with the lid closed** and the laptop screen off during the boot and my **desktop panels and wallpaper are gone**.

Looks like connected to screen setup detected by KDE.

>>>

[1]: https://forum.manjaro.org/t/manjaro-kde-taskbar-panel-missing-each-time-i-log-into-account-after-log-off-or-reboot-event/145960/7
Comment 31 tmdm 2020-07-16 17:14:09 UTC
I always have the laptop lid open. I never close the lid :) But I have this problem even after reinstalling Manjaro KDE. And in the same way, I have 2 operating systems on a laptop. Windows 10 and Manjaro KDE.
Comment 32 Evgenii Frolov 2020-07-20 05:22:32 UTC
(In reply to grego from comment #30)
> I started to experience exactly the same issue, hovewer, in my case I found
> a way to reproduce it. I commented on that already on Manjaro forum [1] so
> here's the copy of my findings:
> 
> >>>
> I experienced the same issue today i.e. after a reboot my default panel has
> gone and I could not add it back nor any other panel via the context menu,
> the desktop wallpaper has reset to the default and my custom key bindings
> for the default panel have been gone equally.
> 
> I think I identified it to be related to my dual screen setup. My Lenovo
> L570 has a UHD 4K display connected via a mini-DP to DP cable. As I used to
> dual boot with Windows 10 I had the laptop lid open during boot and closed
> it when the login screen came on. This resulted in a cloned display on both
> the laptop and the 4K screen with the same low resolution of the laptop
> screen. After logging in the resolution gets adjusted to 4K and scaling of
> 150% is applied.
> 
> Today, however, I restarted from Windows 10 with the lid closed and the boot
> continued only on the 4K screen. When KDE login screen came up it was in the
> native 4K resolution without any scaling applied and after logging in my
> desktop was reset, the default panel gone etc. The same remained after
> logging out and in again, rebooting and even clearing cache, config files
> and applying other reset actions I was able to find. Resetting the theme to
> defaults helped bring the default panel back but it didn't persist the log
> out/in nor reboot cycle. Very frustrating.
> 
> Finally, I booted up with the laptop lid open and… bang! my panel was there
> back again. I repeated the same procedure a few times with the same result:
> 
> - **reboot with the lid open** and the laptop screen on during the boot and
> my **desktop and panels persist**
> - **reboot with the lid closed** and the laptop screen off during the boot
> and my **desktop panels and wallpaper are gone**.
> 
> Looks like connected to screen setup detected by KDE.
> 
> >>>
> 
> [1]:
> https://forum.manjaro.org/t/manjaro-kde-taskbar-panel-missing-each-time-i-
> log-into-account-after-log-off-or-reboot-event/145960/7

I can confirm that I can reproduce the issue with laptop and additional monitor following these steps.
Comment 33 Alberto 2020-07-30 17:51:21 UTC
Hi, I have the same problem here, with the kubuntu 20.04 that I've installed yesterday. I have no idea what it happening, but it may be useful to indicate that I've also had problems with the dialog that is opened to switch among connected screens (fn+F8 in my laptop), appeared frequently (same than here: https://www.reddit.com/r/Kubuntu/comments/g7szxk/switch_to_external_screen_bug/), and I had to disable kscreen2.
Comment 34 Matt 2020-08-28 07:17:40 UTC
I have the same issue: panel does not show up when an external monitor is connected. Panel can't even be added. I have to log out of plasma, disconnect the external monitor, log in and then connect the external monitor again.

ACTUAL system software:
Operating System: openSUSE Leap 15.2
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.71.0
Qt Version: 5.12.7
Kernel Version: 5.3.18-lp152.33-default
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-4300U CPU @ 1.90GHz
Memory: 3,5 GiB of RAM

It was mentioned here before that the issue might be related to the plasma-org.kde.plasma.desktop-appletsrc. I observed the file and so far I could only find similarities regarding the [ScreenMapping] section.

In all working setups the screenMapping looked like this:
screenMapping=desktop:/trash.desktop,0,desktop:/Home.desktop,0

In all NOT working setups the screenMapping looked like this:
screenMapping=desktop:/trash.desktop,2,desktop:/Home.desktop,2

Unfortunately I could not find a description of the syntax, so I don't know what the numbers do refer to.

The PreloadWeight variables in the [Containments] sections change back and forth with no obvious pattern to me.
Comment 35 serviceskde 2020-08-28 07:20:53 UTC
The way I see it, the fix for this issue is incredibly simple: Instead of using unstable indexes that are then mapped to actual displays why not specify display directly?

So instead of saving "Panel X is on the screen 4", it would save "Panel X is on the screen DisplayPort-4".
Comment 36 Matt 2020-08-28 07:58:56 UTC
(In reply to matejdro from comment #35)
 
> So instead of saving "Panel X is on the screen 4", it would save "Panel X is
> on the screen DisplayPort-4".

Thanks for the hint. How would you save "Panel X is on the screen DisplayPort-4" exactly? In which KDE dialog/menu would you save that? Is there a setting in the "Display Configuration" dialog for that?

And what happens, if the external monitor is disconnected, e.g. laptop is used stand alone? Do you have to save something different before or is it changed automatically?
Comment 37 serviceskde 2020-08-28 08:03:23 UTC
(In reply to Matt from comment #36)
> (In reply to matejdro from comment #35)
>  
> > So instead of saving "Panel X is on the screen 4", it would save "Panel X is
> > on the screen DisplayPort-4".
> 
> Thanks for the hint. How would you save "Panel X is on the screen
> DisplayPort-4" exactly? In which KDE dialog/menu would you save that? Is
> there a setting in the "Display Configuration" dialog for that?
> 
> And what happens, if the external monitor is disconnected, e.g. laptop is
> used stand alone? Do you have to save something different before or is it
> changed automatically?


Sorry, I wasn't clear enough. That was meant for KDE developers as a way of fixing the bug.

Panels are saved in `~/.config/plasma-org.kde.plasma.desktop-appletsrc`. But lastScreen property of every panel is just a number. Those numbers are mapped in `~/.config/plasmashellrc` under `[ScreenConnectors]`. Trouble is that these mappings change every time display configuration changes, which makes panel positions unstable.
Comment 38 Gunar 2020-09-13 13:17:40 UTC
I have the same problem on a freshly installed kubuntu 20.04.1. As soon as I activate my external monitor as primary the panel is gone and the background picture is set to original. I can fix this by doing "kquitapp5 plasmashell && kstart5 plasmashell &". Everytime I log out or reboot I have to do it again.

KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.7
Kernel Version: 5.4.0-47-generic

How can I help to solve this issue?
Comment 39 me 2020-09-14 10:49:12 UTC
I am experiencing the same problem.

Manjaro Version: 20.1
Kernel: 5.8.6-1-MANJARO
Plasma Version: 5.19.5

Laptop: T480s
Thinkpad Thunderbolt dock
ThinkVision monitor

I boot up my computer with the lid closed. It is connected to a thunderbolt dock which has a monitor connected to it via Display Port. Once I enter my password into SDDM, I am presented with a black screen and no panel. I am still able to launch applications by using krunner, though.

I can run "kquitapp5 plasmashell && kstart5 plasmashell" to get everything up and going again.

I can't remember exactly when this started happening, but up until (relatively) recently this has never been a problem. If I had to guess, I would say up until about 2 months ago this had never been a problem - everything functioned exactly as one would want it to.


Is there any information on when this issue will be addressed and a fix released?
Comment 40 Alain Knaff 2020-09-16 17:55:52 UTC
I am experiencing the same problem.

Debian Version: 10
Kernel: 4.19.0-10-amd64
Plasma Version: 5.14.5-1

Desktop: Terra
Monitors: 2 Terra 2463W monitors, connected via Display Port

These are monitors that have 2 inputs each, Display Port and HDMI. On Mondays and Fridays, I work from home, and connect my work laptop to the HDMI inputs. The home computer is still connected to the display port inputs, but the monitors are switched to HDMI input.

I've got the impression that the problem mostly occurs when the work computer is connected, and has the screens.

When that happens, the ~/.config/plasmashellrc gets an extra :0.0 entry for the screen connector:

Before:
[ScreenConnectors]
0=DP-1
1=DP-2

After:
[ScreenConnectors]
0=DP-1
1=:0.0
2=DP-2

=> i.e. the bogus sneaked right into the middle of the real entries, causing DP-2 to get renumbered from 1 to 2.

However, the lastScreen settings in .config/plasma-org.kde.plasma.desktop-appletsrc would not get updated, i.e. all panels on DP-2 would still keep lastScreen=1, causing them to disappear (as plasma tried to display them on the non-existant :0.0 screen)


N.B. monitors just going to sleep don't cause the problem by itself (unless ~/.config/plasmashellrc is already corrupted), it actually needs monitor's input to be switched to another computer to make .plasmashellrc to become corrupted. But once plasmashellrc *is* corrupted, then shenanigans happen whenever monitors go to sleep.

I've now write-protected the plasmashellrc file, let's see whether this stops the problem from happening next Friday :-)
Comment 41 Mika Norén 2020-09-21 11:18:53 UTC
(In reply to Alain Knaff from comment #40)
> I am experiencing the same problem.
> 
> Debian Version: 10
> Kernel: 4.19.0-10-amd64
> Plasma Version: 5.14.5-1
> 
> Desktop: Terra
> Monitors: 2 Terra 2463W monitors, connected via Display Port
> 
> These are monitors that have 2 inputs each, Display Port and HDMI. On
> Mondays and Fridays, I work from home, and connect my work laptop to the
> HDMI inputs. The home computer is still connected to the display port
> inputs, but the monitors are switched to HDMI input.
> 
> I've got the impression that the problem mostly occurs when the work
> computer is connected, and has the screens.
> 
> When that happens, the ~/.config/plasmashellrc gets an extra :0.0 entry for
> the screen connector:
> 
> Before:
> [ScreenConnectors]
> 0=DP-1
> 1=DP-2
> 
> After:
> [ScreenConnectors]
> 0=DP-1
> 1=:0.0
> 2=DP-2
> 
> => i.e. the bogus sneaked right into the middle of the real entries, causing
> DP-2 to get renumbered from 1 to 2.
> 
> However, the lastScreen settings in
> .config/plasma-org.kde.plasma.desktop-appletsrc would not get updated, i.e.
> all panels on DP-2 would still keep lastScreen=1, causing them to disappear
> (as plasma tried to display them on the non-existant :0.0 screen)
> 
> 
> N.B. monitors just going to sleep don't cause the problem by itself (unless
> ~/.config/plasmashellrc is already corrupted), it actually needs monitor's
> input to be switched to another computer to make .plasmashellrc to become
> corrupted. But once plasmashellrc *is* corrupted, then shenanigans happen
> whenever monitors go to sleep.
> 
> I've now write-protected the plasmashellrc file, let's see whether this
> stops the problem from happening next Friday :-)

Write-protecting the file only helps to some degree.
The incorrect detection of non-existent displays will still occur and cause displays to jumble around. But as the config remains intact one simply have to perform a "plasmashell --replace" a few times until it's back where it's supposed to be again. Be patient though. Plasmashell will complain about the config file being write-protected, and might even appear as if it has hanged for a few seconds. But it'll come around eventually. Just give it a little time to recover out of the "shock".
Comment 42 Alain Knaff 2020-09-23 20:30:39 UTC
(In reply to Alain Knaff from comment #40)
[...]
> I've got the impression that the problem mostly occurs when the work
> computer is connected, and has the screens.

After some time passed, the pattern of failure apparently has changed for a mysterious reason. Now, the problem happens with the screens going just to sleep. No matter of restoring the config files from backups from various dates cured the problem... Unless there are config files elsewhere than in in ~/.config that need restoring?

Btw, what is the purpose of this mysterious :0.0 entry being added to the ScreenConnectors? Why is it being added *in*the*middle* rather than at the end? And if the purpose of this entry is irrelevant for most use cases anyways, can't we have a config option to just disable this behavior? Could an actual developer please chime in here?

Indeed, I'd rather have a couple of clicks to perform once and for all after buying a new screen, rather than having to do that each time the screens wake up.

No, write protecting the plasmashellrc file unfortunately didn't help. And nor did write protecting plasma-org.kde.plasma.desktop-appletsrc
Comment 43 Alain Knaff 2020-09-27 14:31:29 UTC
*** Bug 425897 has been marked as a duplicate of this bug. ***
Comment 44 Alejo 2020-09-29 15:22:53 UTC
I'm having the same issue. Fresh install (yesterday) of Neon. When applying a theme change, my panel dissapeared, then, following some of the comments here, deleted my plasma-org.kde.plasma.desktop-appletsrc file, which after running kquitapp5 plasmashell && kstart5 plasmashell & got my panel back.
After that, I changed the applications menu for a dashboard, and when I pressed the super key, the panel became unresponsive. Didn't dissapeared, but didn't react to any right or left click. Yet my trackpad worked fine in the rest of the screen. 
I repeated the operation: deleted the file, restarted the panel, yet it didn't worked as expected, but it did after a reboot.
Now I changed again the app menu for a dashboard and it works fine. I'm using a Lenovo Ideapad 120S. I'm NOT using dual monitors as seems to be tha case of all the other comments.
Comment 45 Yurii-Stefan Zhydetskyi 2020-11-09 15:55:36 UTC
I have the same problem and here are what I have found.

Operating System: KDE neon 5.20
KDE Plasma Version: 5.20.2
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.0
Kernel Version: 5.4.0-52-generic
OS Type: 64-bit

I have a laptop and two external screens plugged via a docking station.
Laptop screen I always keep closed and disabled.

Here is what I have in the plasmashellrc file in the [ScreenConnectors] section, just after installing the system:
0=VGA-1     <-- external screen that Plasma sets as a primary screen 
1=eDP-1     <-- laptop's screen
2=HDMI-3    <-- external screen

1)  I added the default panel to the second screen, rebooted the computer. Everything works fine.

2)  After I had disconnected the laptop from the docking station and had turned it on, the plasmashellrc file was changed.
0=eDP-1
1=:0.0
2=VGA-1
3=HDMI-3

3)  Had returned the laptop to the station.
0=VGA-1
1=eDP-1
2=:0.0
3=HDMI-3
Obviously that on this step I reproduce the defect: the panel on the second screen disappeared.

4)  Disconnected the laptop from the docking station again, turned it on and connected TV via HDMI.
TV was added to the end of the list. So I got hope that the panel on my second screen won't be broken again.
But after returning laptop to the docking station I got
0=VGA-1
1=eDP-1
2=:0.0
3=HDMI-1   <-- TV
4=HDMI-3   <-- external screen

I don't know why, but my second screen is always at the end of the list.

5)  Now I won't be faced with the problem until I will have plugged to my laptop some new screen 


OTHER SIDE

There is a way to have the defect constantly.

Set as a primary screen not the screen that was by default assigned as primary.
After that VGA-1 and eDP-1 starts to swapping places every time I reboot my computer.
The behavior is so strange.
It lasts while I don't change the primary screen back, or enable the laptop screen.


ABOUT MANUAL MODIFYING THE plasmashellrc FILE

1) You can remove from the list any screen, but it'll come back after you'll have plugged it again.
2) You can change the order of the list and it'll work even after rebooting, but it'll be returned after you'll have changed the list of the enabled screens. (etc. Disconnect some screen, disconnect the laptop from the docking station, connect TV via HDMI)
3) You can't remove from the list the screen that is available now. Plasma just will restore the last working version of the file. The same will happen if you move the primary screen from 0 position.
Comment 46 s.v.savenko 2020-11-09 19:38:38 UTC
I found the solution. I switched to LXQt and the problem is somehow gone!
Comment 48 Nate Graham 2020-12-03 17:06:31 UTC
Cool, was that ever submitted as a merge request?
Comment 49 Mika Norén 2020-12-28 17:46:34 UTC
(In reply to Nate Graham from comment #48)
> Cool, was that ever submitted as a merge request?

I believe it has, but no one has looked at it yet.
Comment 50 Carlo 2020-12-28 19:13:12 UTC
Yes, it was submitted here: https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/352
Comment 51 Nate Graham 2020-12-31 01:28:24 UTC
Marking as a dupe of the bug that will be fixed once that merge request is merged.

*** This bug has been marked as a duplicate of bug 427278 ***
Comment 52 Erik Quaeghebeur 2022-05-18 11:17:43 UTC
(In reply to Nate Graham from comment #51)
> Marking as a dupe of the bug that will be fixed once that merge request is
> merged.
> 
> *** This bug has been marked as a duplicate of bug 427278 ***

Well, that other bug is marked as fixed. However, I'm still getting this(?) issue with Plasma 5.24.4. Something had crashed my desktop and after rebooting, the panel was gone again. (Laptop + external monitor present, only external one used.)

Please reopen and undo ‘mark as duplicate’. It is not fixed and does not seem to be a duplicate.