After some heavy use, I can't shut down or log out.

It becomes a blackscreen with a movable mouse cursor. "Ctrl+alt+del" will give me again a log out confirmation dialogue.

plasma 5, opensuse leap.

If you've a frozen cursor (you can see it, but it doesn't react to input (and you ensured the wire didn't just drop out of the USB slot that means the X11 server processes no input (and apparently nothing else) or the scanout buffer is frozen (problem in the graphics driver)

=> do you get past the splash screen before things freeze, or soes it freeze in the splash screen?

As general advise on the free radeon driver, check /var/log/Xorg.0.log on whether it uses "GLAMOR" acceleration, if yes, try EXA:
/etc/X11/xorg.conf.d/20-radeon.conf

Code: Select all

Section "Device"
   Identifier  "AMD R9 270X"
   Driver   "radeon"
   Option   "AccelMethod"           "EXA"
EndSection