Bug 514276

Summary:	Heavy Flickering on Second Display with NVIDIA Proprietary Drivers using Plasma Login Manager
Product:	[Plasma] kwin	Reporter:	agarplayerarlon
Component:	general	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	NEEDSINFO WAITINGFORINFO
Severity:	normal	CC:	kde, olib141
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	picture of the issue journalctl logs dmesg nvidia logs

Description agarplayerarlon 2026-01-07 13:51:27 UTC

Created attachment 188289 [details]
picture of the issue

SUMMARY
I've already reported this bug on SDDM github months ago but it never got an answer (https://github.com/sddm/sddm/issues/2123), and since Plasma Login Manager is a fork of SDDM I thought it could be affected by the same nasty bug, which it is.
I'm on Arch Linux with the latest nvidia drivers 590.48.01 and I've installed Plasma Login Manager from the AUR and followed the instructions on the official gitlab page to enable it (https://invent.kde.org/plasma/plasma-login-manager).

Also I want to specify that this issue doesn't happen with GDM, and it didn't happen with SDDM running on x11, it only happened with SDDM running on Wayland.

So basically I have two monitors, and the second monitor becomes a flickery mess most of the times after I log in from Plasma Login Manager, while the first monitor is normal, and the heavy flickering also appears on the login session itself, not just after logging in, I've attached a picture of how it looks on my second monitor.

STEPS TO REPRODUCE
1. Login from Plasma Login Manager

OBSERVED RESULT
Heavy flickering on the second monitor


EXPECTED RESULT
No flickering on the second monitor.


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux
KDE Plasma Version: 6.5.4
KDE Frameworks Version: 6.21.0
Qt Version: 6.10.1

ADDITIONAL INFORMATION

Comment 1 Oliver Beard 2026-01-07 14:37:55 UTC

SDDM configured to use Wayland uses KWin, as does plasma-login-manager. This would seem to be a KWin issue.

Is the Plasma Wayland session affected?

As well, any suspicious journal output when this happens would be useful. The nvidia driver is generally noisy when things go wrong.

Comment 2 Oliver Beard 2026-01-07 14:40:38 UTC

Sorry, I did not read enough.

Can you clarify when this is happening? It seems like you're saying it happens after login, but you also describe it happening on the login screen itself.

Comment 3 agarplayerarlon 2026-01-07 14:46:52 UTC

(In reply to Oliver Beard from comment #2)
> Sorry, I did not read enough.
> 
> Can you clarify when this is happening? It seems like you're saying it
> happens after login, but you also describe it happening on the login screen
> itself.

yes, it happens both on the login screen and after login, and the only way to stop it is to turn off the second monitor and turning it back on, but then once I log out the flickering comes back on the second monitor in the login screen and keeps being there after logging in.

If I turn on the computer with both of the monitors being turned on, then the first time I land in the login screen there is no flickering, and if I log in for the first time it seems that the flickering doesn't happen (although I have to test this more), but after I log out for the first time the flickering starts on the login screen and stays after logging in.

Comment 4 Oliver Beard 2026-01-07 14:49:47 UTC

From the info provided I'll move this to KWin for those folks to investigate.

Comment 5 agarplayerarlon 2026-01-07 14:54:28 UTC

(In reply to Oliver Beard from comment #4)
> From the info provided I'll move this to KWin for those folks to investigate.

thanks for the help, now I'll attach the logs you asked from journalctl

Comment 6 agarplayerarlon 2026-01-07 14:55:53 UTC

Created attachment 188293 [details]
journalctl logs

Comment 7 agarplayerarlon 2026-01-07 14:58:35 UTC

Created attachment 188294 [details]
dmesg nvidia logs