PMPD

Ive gotten a pretty big bug where my huge fort i had with walls boarded windows everything is now overrun with zombies now that i updated to the new version and i got killed. I thankfully backed up my save but is there a way to prevent it from happening? I'm using the steam version and is there a way to just revert to the previous build? This didn't happen upon updating to any of the other builds and my survival time is 3 months.