Hey!
I can only tell you about the exception file you provided.
The error happens in the State Component which is assigned to every script object in the game (anything you can click on - chair, Sim, table, etc.). In your case, it's about adding a Sim (ID: 493994472144306196) object to the world and failing to define an initial value of a state base on a statistic of that Sim.
The state that is being set it based on a statistic of that Sim. The related statistic is missing from that Sim statistics tracker. Now, I don't know how your mod works, but it could be that you're referring to a statistic somewhere that does not exist anymore.
It's hard to tell much about it but it could be that the state stops working once it knows that the statistic doesn't exist anymore after loading the game so any future or new saves don't have that problem.
Look through your tuning files, search for 'linked_stat' value, it might be set wrong.
