Bug 514632

Summary:	1/3 monitor stays black on KDE initialization AFTER login on boot
Product:	[Plasma] kwin	Reporter:	Avasam <samuel.06>
Component:	multi-screen	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	REOPENED ---
Severity:	normal	CC:	kdedev, nicolas.fella
Priority:	NOR	Keywords:	X11-only
Version First Reported In:	5.27.12
Target Milestone:	---
Platform:	Pop!_OS
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	Video demonstrating the blank screen + workarond

Description Avasam 2026-01-15 04:38:28 UTC

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SUMMARY

When I boot my computer, I see all 3 of my monitors on the Pop!_OS Cosmic login screen.

After logging in, I see the KDE splash screen on only 2 monitors. Once KDE is done loading, the only way I found so far of fixing my third, vertical monitor (plugged through DVI) to show anything, is to change a Display setting (for example I change the display orientation, then revert the change).

STEPS TO REPRODUCE
1. Boot
2. Login (Cosmic login screen)


OBSERVED RESULT

See that 1/3 monitor (vertical one through DVI, in case that matters) is blank (backlight and signal, but all black). No mouse visible but I can move windows / my mouse over to the blank monitor (nothing is visible, but my monitor is at least correctly picked-up as existing)

EXPECTED RESULT

I expect to see my desktop

SOFTWARE/OS VERSIONS
Operating System: Pop!_OS 24.04
KDE Plasma Version: 5.27.12
KDE Frameworks Version: 5.115.0
Qt Version: 5.15.13
Kernel Version: 6.17.9-76061709-generic (64-bit)
Graphics Platform: offscreen
Processors: 16 × AMD Ryzen 7 5800X 8-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 3070/PCIe/SSE2

ADDITIONAL INFORMATION

This is a fairly fresh Linux install. My issue started happening as soon as I installed KDE. Which I did by running `sudo apt install kde-standard` (and selecting to keep Cosmic as the login page)

Similar issues:
- https://bugs.kde.org/show_bug.cgi?id=490040 Description and title is spot on to my issue. Except that restarting plasmashell does not help.
- https://bugs.kde.org/show_bug.cgi?id=509763
- https://bugs.kde.org/show_bug.cgi?id=475238 Not very descriptive, but I have A black screen after login

Comment 1 Avasam 2026-01-15 04:39:32 UTC

I meant HDMI, not DVI. I can't find how to edit my post

Comment 2 Avasam 2026-01-15 04:43:23 UTC

Created attachment 188543 [details]
Video demonstrating the blank screen + workarond

Comment 3 Avasam 2026-01-15 04:58:55 UTC

Another similar issue: https://bugs.kde.org/show_bug.cgi?id=465001
I can also work around the bug with a sleep/wake cycle. However I can't replicate it by simply reconnecting a cable.

Comment 4 Nicolas Fella 2026-01-19 11:52:37 UTC

Thank you for your bug report!

However Plasma 5.27 no longer receives updates or maintenance from KDE; active versions are 6.5 or newer. Please upgrade to an active version as soon as your distribution makes it available to you. Plasma is a fast-moving project, and bugs in one version are often fixed in the next one.
If you need help with Plasma 5.27, please contact your distribution, who bears the responsibility of providing help for older releases that are no longer receiving updates from KDE.

If you can reproduce the issue after upgrading to an active version, feel free to re-open this bug report.

Thanks for understanding!

Comment 5 Avasam 2026-01-22 02:28:42 UTC

Thanks for the thoughtful response.

I am now on the following, and still having the issue.
Operating System: Kubuntu 25.10
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.17.0
Qt Version: 6.9.2
Kernel Version: 6.17.0-8-generic (64-bit)
Graphics Platform: X11
Processors: 16 × AMD Ryzen 7 5800X 8-Core Processor
Memory: 32 GiB of RAM (31.3 GiB usable)
Graphics Processor: NVIDIA GeForce RTX 3070

I know 6.4.5 is not 6.5 which you said is active. But I'm still writing it here for tracking purposes and in case something goes horribly wrong trying to update to 6.5.

Comment 6 Avasam 2026-01-22 03:17:00 UTC

Two new updates
1. Still happens on KDE 6.5
2. Sometimes, very rarely and randomly, my 2nd (horizontal) screen is also blacked out. Still consistent on the 3rd (vertical) screen.
2. I think this is an X11 specific issue. I don't remember having the issue on Kubuntu (which now ships wayland only) until I reinstalled X11. If I boot in Wayland (no issue), then logout user, then switch to a X11 session, the issue does present itself.

Unfortunately, Wayland is still unusable for my needs (OBS browser sources and docks not working with it) + the cursor is very laggy in Wayland.

Updated specs:
Operating System: Kubuntu 25.10
KDE Plasma Version: 6.5.5
KDE Frameworks Version: 6.20.0
Qt Version: 6.9.2
Kernel Version: 6.17.0-8-generic (64-bit)
Graphics Platform: X11
Processors: 16 × AMD Ryzen 7 5800X 8-Core Processor
Memory: 32 GiB of RAM (31.3 GiB usable)
Graphics Processor: NVIDIA GeForce RTX 3070