I have a dual monitor setup, since I think version 5.15.0 (sorry i can t be more precise) one stopped working correctly.
It work fine in SDDM, but as soon as i login it became black, and i can see only the mouse; trying to drag a windows there, it will show only the mouse. Turning off and on the monitor fix it, and it start work normally.
This secondary monitor also is in vertical mode.
Before this version it was working 100% of the times
STEPS TO REPRODUCE
1. turn on pc
2. log into sddm
the secondary vertical monitor goes black, but the mouse still can be seen; no desktop, icons, widget or windows. Turning the monitor off and on fixes it
my normal desktop
arch linux, probably the issue is from a couple of month (today is 2019-10-22), on xorg
worked fine for many month.
Using a nVidia card, with proprietary driver.
part of 3 bug report: 413326 413328 413329
fixed by deleting the kscreen folder under ~/.local/share; looks like even if I enable/disable the monitors and change the conf, something broken get carried over.
I think proper fix should be to find the problematic configuration and get rid of it at load time
*** This bug has been marked as a duplicate of bug 353975 ***