After a reboot it seems to be working. Unfortunately since I was in the middle of getting everything setup I am not sure exactly what fixed it but since I didn’t change much in the way of config, it is most likely all the proper video drivers being installed.
I get a similar bug, but very inconsistently. When my monitors turn off due to being idle, or when I reboot, there is a small, about 1%, chance that my wallpaper will reset to the default one, and sometimes the two displays get switched. I notice it at least once a month, but I don’t know how to reproduce it myself.
Unfortunatelly, Plasma (AI) thinks that it is smart enough to auto configure displays, listening to hardware changes.
These issues point to this, that one or more monitor are supposed to be disconnected, so Plasma uses the default configuration for a new monitor, creating a new hash as a MonitorID. Some time ago, it was using ~/.cache/ related data, which I don’t know if it still uses them, or how.
Most frequent issues are usually with DP/DisplayPort connected H/W, which seem to produce some behavior very close to being disconnected, when going for PM sleep.
In such or similar cases, a relevant workaround that would either don’t let them sleep, or block Plasma from auto-configuring, might help, but I have not tried any, when using Plasma. Instead I had chosen to switch to bspwm, to have complete control of my DE .
Standard control freak situation!