Comment # 20 on bug 1028575 from Mircea Kitsune

Very important note: While investigating a completely unrelated bug, I
remembered that KWin was configured to use egl over glx on my machine. I
believe glx is the old render architecture, whereas egl is the new renderer
which uses OpenGL and is visibly a lot faster.

Considering that desktop activity was always the cause of the freezes in some
form, I have a strong suspicion that this might have something to do with the
GPU freezes as well! It's a very likely candidate because egl involves
experimental OpenGL rendering, and since it's not enabled by default that would
also explain why few other people are able to reproduce the GPU lockups. I have
just now switched back to glx and therefore haven't had the time to confirm
this, but I'm willing to bet it just might make the problem go away... I will
immediately post an update if and when I'm proven wrong obviously.

If anyone else wants to test this theory and help in reproducing the system
freeze, consider switching to egl rendering. Obviously this means your machine
might start freezing as well, so only do this if there's no risk of data loss
or major annoyance. The switch is done by opening ~/.config/kwinrc in a text
editor and changing:

GLPlatformInterface=egl

to

GLPlatformInterface=glx

Note that if you're using an Aurorae theme, you might experience the bug I
mentioned above, which involves KWin no longer rendering window decorations.
Here are the reports for that in case anyone is curious:

https://bugzilla.opensuse.org/show_bug.cgi?id=1033598
https://bugs.kde.org/show_bug.cgi?id=378663