The wallpaper on a secondary monitor will disappear on reboot/power off, leaving a black background. It can be restored in "System Settings" by temporarily making the secondary monitor the primary.
STEPS TO REPRODUCE
1. Have a system with multiple monitors.
2. Have a wallpaper in the background on each monitor
3. Restart system several times, perhaps powering off.
The monitor that is the secondary monitor will have a black background. The wallpaper can be restored by making the secondary monitor the primary, pressing "Apply."
Both monitors should retain their backgrounds to the previously set values on restart/power off.
(available in About System)
KDE Plasma Version:
KDE Frameworks Version:
What kind of GPU are you using?
It's an Nvidia GTX 1050 Ti.
I would be surprised if it's a hardware problem. Seems to me like a problem with the "restore the wallpaper on the secondary monitor(s) code."
In this case I think it's actually not a hardware issue. :) Some AMD GPUs trigger a kernel bug that causes issues like this, but NVIDIA GPUs don't have the same problem. It is more likely to be a software issue on our side.
If you right-click on the black background, do you see a context menu? Can you move desktop icons there? Was there a panel there too that inappropriately moved elsewhere
Right clicking does NOT bring up a context menu.
I can move icons over to the black background, but they aren't visible there. Interestingly, I don't think there were any icons on either screen initially, but they appeared later, when I right clicked on the wallpaper.
I don't believe there were ever any panels on that monitor.
Ah oh, so it's not just that the wallpaper went missing--the whole containment is missing.
Can you check in the Display Configuration KCM whether or not one of your screens is slightly overlapping the other one--even by just one pixel? If so, this is Bug 391531.
I have used KDE for a long time but I'm not too familiar with the internals.
I used the Nvidia X Server settings to identify positions. The monitors are 1680 x 1050. The secondary monitor is at 0,0. The primary is at 1680, 0. That doesn't seem to be an overlap. I don't know how to get into the KCM settings you asked for. I hope this answers your question.
Thanks for the info. If there's no overlay, then this is in fact Bug 371717.
*** This bug has been marked as a duplicate of bug 371717 ***
*** This bug has been marked as a duplicate of bug 442826 ***
*** This bug has been marked as a duplicate of bug 353975 ***