[2020] Pak file corrupt or tampered with. Please use steam option “verify integrity of game files” to repair game install. Exiting…

Hey @vyanie

This particular issue seems to be isolated and might possibly be related to mods, considering what you mentioned in step 5. As a general workaround we recommend unsubscribing from all mods and deleting the Steam workshop folder to get rid of any possible corrupted files, checking the integrity of the game files and then, resubscribing to all mods.
On vanilla installations, this issue appears inconsistently and only requires a re-verification of files to get rid of it. That issue in particular is known by the team but we’re still looking for a reliable repro case, since it seems to strike at random. But it doesn’t affect gameplay the way you described in your particular situation.