Okay so I just tried it, same thing happened - just tried going into closest neighbouring building where I know there should be zombies. The console bar popped up with a thousand "null reference exceptions" and screen froze. Used Task Manager to end process, removed zombie mod, restarted game. In the same building, no console appears, no crash, zombies spawned as expected.
Uploaded my log file for you in case that helps.
output_log__2020-09-20__19-05-53.txt