(In reply to Roman from comment #0)
> When I start plasma, I see ksplash, but when it dissapear I see that plasma
> still downloading(black screen, then wallpaper and widgets). When I start
> plasma with openbox, I have another issue - ksplash loading is longer than
> should be.
> 
> Reproducible: Always
> 
> 
> 
> 
> .xserver-errors
> startkde: Starting up...
> Service started, version: 6.2.0
> Baloo File Indexing has been disabled
> Не вдається відкрити бібліотеку «/usr/lib/libkdeinit5_lib/kdeconnectd».
> Cannot load library /usr/lib/libkdeinit5_lib/kdeconnectd:
> (/usr/lib/libkdeinit5_lib/libkdeconnectd.so: не вдалося відкрити файл
> об’єктів спільного використання: Немає такого файла або каталогу)
> OpenGL vendor string:                   NVIDIA Corporation
> OpenGL renderer string:                 GeForce GT 740/PCIe/SSE2
> OpenGL version string:                  4.5.0 NVIDIA 358.16
> OpenGL shading language version string: 4.50 NVIDIA
> Driver:                                 NVIDIA
> Driver version:                         358.16
> GPU class:                              Unknown
> OpenGL version:                         4.5
> GLSL version:                           4.50
> X server version:                       1.18
> Linux kernel version:                   4.2.5
> Requires strict binding:                no
> GLSL shaders:                           yes
> Texture NPOT support:                   yes
> Virtual Machine:                        no
> kscreen: Primary output changed from KScreen::Output(Id: 638 , Name: "VGA-0"
> ) ( "VGA-0" ) to KScreen::Output(Id: 638 , Name: "VGA-0" ) ( "VGA-0" )
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> last screen is < 0 so putting containment on screen  0
> QDBusConnection: session D-Bus connection created before QCoreApplication.
> Application may misbehave.
> QDBusConnection: session D-Bus connection created before QCoreApplication.
> Application may misbehave.
> No metadata file in the package, expected it at:
> "/home/bugworm/Картинки//metadata.desktop"
> No metadata file in the package, expected it at:
> "/home/bugworm/Картинки//metadata.desktop"
> No metadata file in the package, expected it at:
> "/home/bugworm/Картинки//metadata.desktop"
> kscreen: Primary output changed from KScreen::Output(Id: 638 , Name: "VGA-0"
> ) ( "VGA-0" ) to KScreen::Output(Id: 638 , Name: "VGA-0" ) ( "VGA-0" )
> Connecting to deprecated signal
> QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
> QDBusConnection: session D-Bus connection created before QCoreApplication.
> Application may misbehave.
> QDBusConnection: session D-Bus connection created before QCoreApplication.
> Application may misbehave.
> kbuildsycoca4 running...
> yakuake(2611)/kdecore (KLibrary) findLibraryInternal: plugins should not
> have a 'lib' prefix: "libkonsolepart.so"
> qml: Reading townStrings from configuration:
> [{"placeAlias":"Dniprodzerzhyns’k","townString":"Ukraina/Dnipropetrovsk/
> Dniprodzerzhyns’k"}]
> QDBusConnection: session D-Bus connection created before QCoreApplication.
> Application may misbehave.
> yakuake(2611)/konsole Konsole::Session::run: Attempted to re-run an already
> running session. 
> QDBusConnection: session D-Bus connection created before QCoreApplication.
> Application may misbehave.
> file:///usr/share/plasma/plasmoids/org.kde.plasma.trash/contents/ui/main.qml:
> 96: ReferenceError: count is not defined
> KActivities: Database connection: 
> "kactivities_db_resources_139806481319936_readonly" 
>     query_only:          QVariant(qlonglong, 1) 
>     journal_mode:        QVariant(QString, "wal") 
>     wal_autocheckpoint:  QVariant(qlonglong, 100) 
>     synchronous:         QVariant(qlonglong, 0)
> qml: Reading townStrings from configuration:
> [{"placeAlias":"Dniprodzerzhyns’k","townString":"Ukraina/Dnipropetrovsk/
> Dniprodzerzhyns’k"}]
> Known plasmoid ids: QHash(("org.kde.plasma.battery",
> 14)("org.kde.plasma.clipboard", 9)("org.kde.plasma.printmanager",
> 11)("org.kde.plasma.devicenotifier", 13)("org.kde.plasma.volume",
> 10)("org.kde.plasma.notifications", 12)("org.kde.plasma.mediacontroller",
> 15))
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> unversioned plugin detected, may result in instability
> QFont::setPointSizeF: Point size <= 0 (0.000000), must be greater than 0
> QFont::setPointSizeF: Point size <= 0 (0.000000), must be greater than 0
> QFont::setPointSizeF: Point size <= 0 (0.000000), must be greater than 0
> QFont::setPointSizeF: Point size <= 0 (0.000000), must be greater than 0
> QFont::setPointSizeF: Point size <= 0 (0.000000), must be greater than 0
> QFont::setPointSizeF: Point size <= 0 (0.000000), must be greater than 0
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollBar.qml:91: TypeError:
> Cannot read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollBar.qml:91: TypeError:
> Cannot read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:114:
> TypeError: Cannot read property 'corner' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:63:
> TypeError: Cannot read property 'padding' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:64:
> TypeError: Cannot read property 'padding' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:65:
> TypeError: Cannot read property 'padding' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:66:
> TypeError: Cannot read property 'padding' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/ScrollView.qml:286: TypeError:
> Cannot read property '__wheelScrollLines' of null
> Notifications service registered
> XSync seems available and ready
> XSync Inited
> Supported, init completed
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:96: TypeError: Cannot
> read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:96: TypeError: Cannot
> read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:106:17: Unable to assign
> [undefined] to QObject*
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:96: TypeError: Cannot
> read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:85: TypeError: Cannot
> read property 'effectivePressed' of undefined
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:106:17: Unable to assign
> [undefined] to QObject*
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:96: TypeError: Cannot
> read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:85: TypeError: Cannot
> read property 'effectivePressed' of undefined
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:106:17: Unable to assign
> [undefined] to QObject*
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:96: TypeError: Cannot
> read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:85: TypeError: Cannot
> read property 'effectivePressed' of undefined
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:106:17: Unable to assign
> [undefined] to QObject*
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:96: TypeError: Cannot
> read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Button.qml:85: TypeError: Cannot
> read property 'effectivePressed' of undefined
> file:///usr/share/plasma/plasmoids/org.kde.plasma.systemtray/contents/ui/
> TaskDelegate.qml:156: TypeError: Cannot read property 'taskItem' of undefined
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> file:///usr/share/plasma/plasmoids/org.kde.plasma.systemtray/contents/ui/
> TaskDelegate.qml:156: TypeError: Cannot read property 'taskItem' of undefined
> file:///usr/share/plasma/plasmoids/org.kde.plasma.systemtray/contents/ui/
> PlasmoidItem.qml:35: TypeError: Type error
> 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.
> Both point size and pixel size set. Using pixel size.
> file:///usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/
> DigitalClock.qml:444:5: QML Text: Cannot anchor to a null item.
> Both point size and pixel size set. Using pixel size.
> Both point size and pixel size set. Using pixel size.
> Plasma Shell startup completed
> Both point size and pixel size set. Using pixel size.
> Both point size and pixel size set. Using pixel size.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> <Unknown File>: QML Plasmoid: Cannot anchor to an item that isn't a parent
> or sibling.
> org.kde.plasma.pulseaudio: Attempting connection to PulseAudio sound daemon
> org.kde.plasma.pulseaudio: QHash((258, "PulseObject")(259,
> "ObjectName")(257, "Index")(270, "ActivePortIndex")(268, "CardIndex")(269,
> "Ports")(266, "Name")(267, "Description")(264, "HasVolume")(265,
> "VolumeWritable")(262, "Volume")(263, "Muted")(260, "Index")(261,
> "Properties"))
> org.kde.plasma.pulseaudio: QHash((258, "PulseObject")(259,
> "ObjectName")(257, "Index")(270, "ActivePortIndex")(268, "CardIndex")(269,
> "Ports")(266, "Name")(267, "Description")(264, "HasVolume")(265,
> "VolumeWritable")(262, "Volume")(263, "Muted")(260, "Index")(261,
> "Properties"))
> file:///usr/lib/qt/qml/org/kde/plasma/extras/ScrollArea.qml:48: Error:
> Cannot assign to non-existent property "interactive"
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollBar.qml:91: TypeError:
> Cannot read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollBar.qml:91: TypeError:
> Cannot read property of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:114:
> TypeError: Cannot read property 'corner' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:63:
> TypeError: Cannot read property 'padding' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:64:
> TypeError: Cannot read property 'padding' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:65:
> TypeError: Cannot read property 'padding' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/Private/ScrollViewHelper.qml:66:
> TypeError: Cannot read property 'padding' of null
> file:///usr/lib/qt/qml/QtQuick/Controls/ScrollView.qml:286: TypeError:
> Cannot read property '__wheelScrollLines' of null
> Both point size and pixel size set. Using pixel size.
> Both point size and pixel size set. Using pixel size.
> qml: iconName: 4
> qml: iconName: 1
> qml: wind direction: NE
> org.kde.plasma.pulseaudio: state callback
> Both point size and pixel size set. Using pixel size.
> Both point size and pixel size set. Using pixel size.
> org.kde.plasma.pulseaudio: state callback
> org.kde.plasma.pulseaudio: state callback
> org.kde.plasma.pulseaudio: ready
> kscreen: Primary output changed from KScreen::Output(Id: 638 , Name: "VGA-0"
> ) ( "VGA-0" ) to KScreen::Output(Id: 638 , Name: "VGA-0" ) ( "VGA-0" )
> kscreen: Primary output changed from KScreen::Output(Id: 638 , Name: "VGA-0"
> ) ( "VGA-0" ) to KScreen::Output(Id: 638 , Name: "VGA-0" ) ( "VGA-0" )
> file:///usr/share/plasma/plasmoids/org.kde.plasma.volume/contents/ui/main.
> qml: QML Plasmoid: Cannot anchor to an item that isn't a parent or sibling.
> file:///usr/share/plasma/plasmoids/org.kde.plasma.volume/contents/ui/main.
> qml: QML Plasmoid: Cannot anchor to an item that isn't a parent or sibling.
> file:///usr/share/plasma/plasmoids/org.kde.plasma.volume/contents/ui/main.
> qml: QML Plasmoid: Cannot anchor to an item that isn't a parent or sibling.
> file:///usr/share/plasma/plasmoids/org.kde.plasma.volume/contents/ui/main.
> qml: QML Plasmoid: Cannot anchor to an item that isn't a parent or sibling.
> file:///usr/lib/qt/qml/org/kde/plasma/extras/ScrollArea.qml:48: Error:
> Cannot assign to non-existent property "interactive"
> file:///usr/lib/qt/qml/org/kde/plasma/extras/ScrollArea.qml:48: Error:
> Cannot assign to non-existent property "interactive"
> file:///usr/share/plasma/plasmoids/org.kde.plasma.kicker/contents/ui/
> DashboardRepresentation.qml:295:17: QML Heading: Binding loop detected for
> property "height"
> qml: iconName: 4
> qml: iconName: 1
> qml: wind direction: NE
> qml: iconName: 4
> qml: iconName: 4
> qml: iconName: 1
> qml: wind direction: NE
> trying to show an empty dialog
> no winId: probably startup task
> created new desk group
> created new desk group
> kscreen: Primary output changed from KScreen::Output(Id: 638 , Name: "VGA-0"
> ) ( "VGA-0" ) to KScreen::Output(Id: 638 , Name: "VGA-0" ) ( "VGA-0" )
> kscreen: Primary output changed from KScreen::Output(Id: 638 , Name: "VGA-0"
> ) ( "VGA-0" ) to KScreen::Output(Id: 638 , Name: "VGA-0" ) ( "VGA-0" )
> kscreen: Primary output changed from KScreen::Output(Id: 638 , Name: "VGA-0"
> ) ( "VGA-0" ) to KScreen::Output(Id: 638 , Name: "VGA-0" ) ( "VGA-0" )
> kscreen: Primary output changed from KScreen::Output(Id: 638 , Name: "VGA-0"
> ) ( "VGA-0" ) to KScreen::Output(Id: 638 , Name: "VGA-0" ) ( "VGA-0" )

As far as I understand, I have the same problem. We use a customized Kubuntu and are developing on the bionic development release. 
Our login-scripts are running in an openbox session that is started before startkde. There I set a background image using feh. When startkde and ksplashqml run, the background image from feh pops up during the splash animation or after it. I test this in a vm using kubuntu 17.10 as a host an virt-manager. On real hardware the problem was less severe - only a short flickering during the splash screen animation was visible.

How I reproduced this in a vm with neon-devedition-gitunstable-20170917-0806-amd64.iso:

1.) Change the color of the Rectangle with id root to "green" in /usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/splash/Splash.qml .
2.) Log off and Log in, look at the splash screen animation.
-> The splash animation has now green background, but a completely black screen appears inbetween the animation.

I am no longer shure that I have the same problem as Roman. But I think I know now what my problem was.

I have used a higher resolution in virt-manager/spice now and then I can see the flickering (or black screen) is the moment where the screen resolution is changed from the low sddm resolution to the high resolution set in kde plasma.

Before I couldn't see that because the resolution in sddm and plasma was equal. Changing resolution in bionic beta would freeze my whole vm that's why I've never done that before.

Would it make sense to set the screen resolution before the splash screen animation starts if that is possible?

I have the same issue.  When ksplash quits I see plasma still loading and widgets not where they shuld have been.  I think this defeats the purpose of a splash screen.

*** Bug 467946 has been marked as a duplicate of this bug. ***

*** Bug 473874 has been marked as a duplicate of this bug. ***

*** Bug 473872 has been marked as a duplicate of this bug. ***

*** Bug 479824 has been marked as a duplicate of this bug. ***

Sadly this is still an issue on git version, its really painfully slow. Doesn't matter if I have ksplash as none, plasmashell loading is still slow....but when I run "pkill plasmashell && kstart plasmashell"  the plasmashell does (re-)run immediately ...so I assume there is some other issue 

----

system spec:

Operating System: openSUSE MicroOS 20240122
KDE Plasma Version: 6.0.80
KDE Frameworks Version: 5.249.0
Qt Version: 6.6.1
Kernel Version: 6.6.11-1-default (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 5700G with Radeon Graphics
Memory: 46.8 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 3060 Ti/PCIe/SSE2