Download Better Exceptions, load the save again, and the name the script file of the offending mod will be at or near the bottom of the Last Exception. The culprit will usually be a script mod whose creator was never expecting EA to ever change arguments for the function "load_data_into_class_instances" because it hasn't been changed in a decade.
It could be any old script mod which adds or modifies interactions, the reward store, buffs, traits, or modifies a sim's needs. This will notably affect almost every single old mod made using Mod Constructor.
