since a few weeks, after almost every login (equals boot, since i log in once after boot and shut down when done) the wallpapers are gone. saved windows are restored, panel is there as well, and so far everything seems to work, just that's there now wallpaper on any of my two monitors. killing and starting plasmashell again makes the wallpapers appear again. so far i have been unable to even find something related in any log.
kde 5.6: still happens occasionally, i need to switch to console and back to force rendering
Do you still get this? Does the context menu on that screen work?
it still sometimes takes a bit longer until the desktop appears, but the origial issue seems to be gone.