I have two 4k displays connected via Displayport, one is rotated by 90 degrees, the other one is my main display.
Sometimes, after I turned off both screens, the lockscreen activated, I turned the displays on again and unlocked the workspace, the wallpaper of the left, rotated display just sets to the color black (or is reset to the default one, then this is is shown in the wallpaper settings). The wallpaper settings menu shows that my actual wallpaper is still selected and I can't set it, I have to set another wallpaper and then the desired one again. I use X11.
STEPS TO REPRODUCE
1. Turn off both screen connected via DP with lockscreen
2. Turn them on again and unlock the workspace
3. Have a look at the left display
Wallpaper is reset or black
Wallpaper remains unchanged
Linux/KDE Plasma: Kubuntu 21.10
(available in About System)
KDE Plasma Version: 5.23.3
KDE Frameworks Version:
Should any further information or logs be required, I'd be happy to help!
*** This bug has been marked as a duplicate of bug 371717 ***
*** This bug has been marked as a duplicate of bug 353975 ***