Custom Background via Windows Group Policy not be applied (Black Background)

Have you got machines or users where the group policy is not applying the custom background, and just black? This is a really easy fix.

You need to amend the file (or delete) “TranscodedWallpaper” to “TranscodedWallpaper.old”
Found here:

\PCNAME\c$\Users\USERNAME\AppData\Roaming\Microsoft\Windows\Themes

Then reboot the device

The file should be re-created and the wallpaper should be working when your user logs in.