If you've got the Missing Downloaded Files error, try this. If so, it's a corrupted temp download file. Is the download stuck there? Perhaps with a 'Missing Downloaded Files' error?
In the Steam Client, check the Downloads page. the fix may be much more simple than that. Are you missing Workshop content? Did you subscribe to things that aren't appearing in the game? Or do they appear in the Content Manager under Workshop Items as Subscribed, but you can't enable or find them under Mods or Assets? Then read on before you try to reinstall your game, Steam, Windows or pay for a program to fix this(don't do this, ever).
