I also had this problem a few days ago, Riverview got corrupted and all the other downloaded store items disappeared. In the end I reinstalled my game as nothing else seemed to work. I assumed I'd managed to do it somehow but I've no idea how as I saved and quit my game and shut down the laptop and when I booted it up the next day it was borked, I didn't even use the laptop in the meantime, let alone touch any of the files.

I'm now using Delphy's installer and playing in SV to try to prevent it happening again but might go back to Riverview, as if it is going to keep happening then I'd like to know.