Looks like to nuke stuff you need to kill three different things now
1.
/steamapps/common/GarrysMod/garrysmod/cache/workshop/2.
/steamapps/workshop/appworkshop_4000.acf3.
/steamapps/workshop/content/4000/4. Quit Steam or restart your computer
If you miss one of the three workshop corrupts and is unfixable until you get all three removed...
This is useful if you're ever trying to unsubscribe from all addons, or if you have a corrupted cache file.