The wallpaper will be reset to black after logout!

[houchen-li]

This only appears on the latest sweet theme.

[angela-d]

My wallpaper was lost on reboot or restart of plasma shell, too.
Even switching away from Sweet, the bug persisted.

Possible cause:

• Use desktop layout from theme: ticked

Behavior:

• After setting that option, even if you change settings (or go to another global theme) later, the bug seems to persist across changes

What fixed it (for me):

• Switching to another global theme
  • Use desktop layout from theme: ticked <--- important step, these seems to undo whatever triggers the bug
• Save and reboot or restart Plasma
  • Desktop stays in place.

While researching this, it appears to be a common KDE bug, there must be a combination of just the right settings in Sweet to trigger it (if activated while using the theme).

Have not tested to see if using Sweet without ticking Use desktop layout from theme triggers the bug.

plasma-org.kde.plasma.desktop-appletsrc lost wallpaper and icon settings on Plasma (re)start.

Left diff is before a shell restart, right is moments after:

Restarting the shell after doing the "fix" mentioned above, the wallpaper stays put.