After manually disable/enable the screen in the Display Configuration the wallpaper reappears again. However, that's sort of pretty annoying everytime on login. Reproducible: Always Actual Results: No wallpaper on one of the screen. Expected Results: Wallpaper should be present.
Not kwin related, it's either a bug in kscreen or plasmashell. To know which: is it really the wallpaper or is there no desktop at all (is there a config button or can you rightclick the "no wallpaper" to get a config menu)?
Well, after login the screen is black. But I can open up a window and drag it onto the black screen. There it is visible and fine. So, everything is fine, except the wallpaper is missing on the screen. When I disable/enable the screen in the Display Configuration then the wallpaper reappears. BUT: when I change the wallpaper in the Desktop Settings, only the Wallpaper of the "good" screen changes. I can't change the Wallpaper of the (once) black screen.
Please inform the plasmashell devs whether there's no desktop window or just no wallpaper. Rightclick the "no wallpaper" area and check whether a popup shows up.
Interesting ... after some experiments and changes I don't recall, the plasmashell works on logout/login/reboot as before. Strange. Well... I set this report to resolved/invalid then. Sorry for the noise.
I have similar issue, but the wallpaper disappears after some time. The screen gets blank. i'll have to check whether the black background reacts to mouse clicks.