I had exactly the same problem on a ThinkPad E16 Gen 4 (Panther Lake),
Kubuntu 26.04.1: coloured garbage and kwin crashes shortly after login,
fewer problems after the first crash.
Cause: it is not a Mesa bug. Probable cause is the Ubuntu-specific kwin
patch. If your user is not in the "video" group, kwin sometimes cannot
open the graphics device on its own right after login, and the patch
then makes kwin and Mesa share it. They get in each other's way, which
causes the corruption and crashes. After the first crash kwin restarts,
and by then the device can be opened normally. That is why it gets
better.
Workaround: add your user to the video and render groups, then reboot:
sudo usermod -aG video,render $USER
For me this fixed it completely: 14 boots over 4 days with no crashes,
no GPU hangs and no corruption, on the same kernel, Mesa and kwin
versions.
Technical details and a proposed fix: LP:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2172530
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https://bugs.launchpad.net/bugs/2168035
Title:
Kwin crash with graphical artefacts just before - Panther lake
Thinkpad X9-15p
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