This is very likely a problem from mods that have not been updated to work with the new game patch yet.
Please unsubscribe from all mods in the Steam Workshop for this game, and delete the folder
C:\Users\<UserName>\AppData\Local\Introversion\Prison Architect\mods\
That may or may not help a prison that's already been affected by the mods, but should stop it happening again.
Then you can start subscribing to mods again, but only ones that have been updated since the patch.
Good luck with that!