Let it do its thing and finish downloading any files it might need.
In the new window, go to the local files tabĬlick on the button that says verify integrity of game files (it might say something else, but you're looking for the keyword VERIFY) In your library, right click on the listing for gmod.
Make sure you have run gmod once already, including loading a map. If you still have their folders downloaded you can load them directly as wallpapers without Steam: https. Those are the mods, maps, tuners downloaded from the workshop. In the referenced folder, the folders in there will be long numbers. Go to the steam folder, go to userdata/some long number/ugc/referenced. Then Steam will stop giving them to Wallpaper Engine, hence the number is lower. SGA seach (the file type for mods, tuners, maps) and found them in a very weird location. Not even older stuff that I had had for a long time. If you are able to find the the 4 missing wallpaper IDs, it may turn out that those were removed or turned invisible by their author or something like that. So I started having a problem ever since there was a new update to gmod that the stuff I was subscribed to wasn't being installed and wasn't showing up in the game. This doesn't have that great of a chance of working anymore. Edit: Guys, this thread is like 5 years old.