We've got a group policy that copies a wallpaper file down to local machines, and a reg key to force the wallpaper to use that file. We doing a breast cancer awareness background, and replaced the file on our file server, which actually does copy down to the workstations, but doesn't seem to actually update the wallpaper. The file name\location are the same. I've ran gpupdate /force, logged off and on, and rebooted the computer.
It seems to update on some computers, not all. Machines are running Windows 7-10.