I currently use two monitors, so I have two separate desktops, with two different wallpapers. Whenever I boot up, they either switch the wallpapers between them or the 2nd monitor has a black wallpaper. Also, the “screen modifier” panel is always much longer than needed:
This happened after a fresh install of Manjaro 20.1, on KDE. Also, don’t know if it matters or something, but I’m on testing branch and I use Materia KDE theme.