The bug just happened to me as well. I do use cheats, but only MCCC and a bit of CC, no other skript mods. I had encountered an outdated skript mod in the same save previously though and taken it out. Also I must admit that I resetted the Sim that turned into a neighbour via debug cheats at least once directly before the bug happened - it was in a thunderstorm and I was annoyed with her always running back inside. Another thing I have in common with previous posters is, that there's infants in my household (and a cat as well. Well, I know the game doesn't like babies and pets). My infants also were causing some minor bugs before this specific bug happened (the usual bug: milestones not getting triggered properly) and I was exiting back into the main menu and reloading the save a couple of times because of it - not sure if that might be another possible cause. Travelling with the affected Sim to another lot and back home fixed it for me immediatly. And another thing I noticed a while before the bug, was that it took the game unusually long to save. As someone who previously also suffered from save corruption, that immediatly triggered enough anxiety to notice the difference. After I managed to solve the bug, this was also back to normal again.
Also, don't tell me please that it's my own fault for using mods or that this bug was caused by them. As someone pointed out earlier, there's been enough console players who experienced this bug as well. I managed to fix it for my save file. I just came here to provide additional information, even though I can't provide a save file.
No, it's def not the cheats/mods/cc, because I'm playing vanilla and am having the same issues. <3
