It is throwing LEs whenever a lot is loaded since the 1.103.250.1020 (For Rent) patch.
According to Tmex's Better Exceptions, the problem is in the game_events.py file.

Been playing with it for several hours and the core functionality works just fine. Just a heads up in case there is an actual major problem.

game_events.py is part of every major game event as it is responsible for making these events accessible to the mod. This doesn't mean it is responsible for the exception.