[Post-Install] kwin_wayland crashed with SIGSEGV. Desktop unusable.

[glhno9]

I've posted this to bugs.kde.org, but maybe someone here can help. Kwin almost always crashes whenever I open the taskbar (I have it hidden), or it needs to paint a new window (e.g. running dolphin, showing a dialog box, etc.).

I added a log from /var/crash to my bug report. Can anyone see the issue? Just upgraded to Kubuntu 25.10 today and I basically can't use it now.

[blackadderkate]

I see from the bug report you have an Nvidia card..

I upgraded my desktop yesterday from 25.04 to 25.10, and wayland was maxing out every single cpu core at 100%..
So I installed X11, which worked a bit better. The CPUs weren't maxing out any more, so it was at least usable, but my Steam games were literally running at 2-3fps because it was using LLVM instead of the Nvidia 570 drivers.

After much faffing aroung, I ended up uninstalling every single Nvidia related package I could find, rebooting, reinstalling them all again and adding nvidia-drm.modeset=1 to the Grub boot options, which seemed to work.

TLDR: I don't think the upgrade process works properly if you have NVIDIA drivers installed.

[glhno9]

Thanks. Yeah I assume it's Nvidia related. I've seen some users of Fedora saying they needed to set nvidia_drm.fbdev=0. I'll try to find some docs on what those things mean and have a fiddle.

I think there is an issue with kwin though because it's only windows/dialogs created by KDE that seem affected. E.g. when I can (finally) launch Firefox, file upload dialogs work fine.