This is most likely mods you are using that are not compatible with the new patch that came out then.
Please try this:
- uninstall PA from Steam
- unsubscribe from all mods in this game's Steam Workshop
Delete the following folders if still present:
- Steam/SteamApps/common/PA
- C:/users/<UserName>/AppData/Local/Introversion/Prison Architect/
(keep any valued save games, of course)
To see the AppData folder you'll need to enable View Hidden Items in File Explorer.
Now install PA again and see how that goes please!