This is something I believe I've only ever encountered once before, and it corrupted my save completely. This seems to be a consistent thing with my saves when I reach the 3rd or so generation with my families, so I'm assuming it's something to do with the save being too old or full or something?

Anyway, I encountered it again last night but thankfully it didn't completely corrupt my save, but I fear it's only a matter of time. I had my Sims try to travel to a specific community lot which they had visited before (I think about 2 IRL days ago) and since then, I have added NO new mods and there have been no new updates. Basically, nothing had changed in terms of mods or custom content, which seems to be the main culprit for this bug from what I'm reading, but I haven't found an awful lot on it. I did some mod updates and batch fixes and that didn't seem to fix it, and I'm hesitant to remove my mods folder completely because it'll basically mess up my save because there's so much CC in there. Once I tried to send them to another lot, it was completely fine. Albeit it was in the same world (the first lot that gave me the error code wasn't).

Thankfully, this wasn't a major thing for me this time. Not travelling to that lot wasn't a huge deal but my main concern right now is if it happens again and I have no recent save to revert to, or if it's a huge deal. As I stated before, the only other times this has happened is when I've been rather far into my families and I'm getting to that point again, so I'm growing concerned.

The best thing to do would probably be to take out the mods and see if you can load an older save. Your save might come up as whacky without your mods but you can resave it as a new save and then go back in with your mods and see if that fixes it. It might be that the game just needs to be clear of cc completely to reset itself