I'm having the same issue with my San Myshuno residents, too! Never with any of the other sims from other worlds. I don't have the same issue if I reset to factory settings. I only had a few mods to begin with, so I've removed them all. I've tried removing all my tray files, all my save files, moved them all back one at a time, different combinations, etc. Nothing has fixed the issue so far. It's frustrating, because that's where I've spent the most time building and developing households.
@NattyElaine When you say you don't have the issue after doing a factory reset, when does it recur? It's worth trying to run one of your existing saves in an otherwise clean Sims 4 folder, as in, do the factory reset, copy over one save, and see how it goes. Since you're copying and pasting the save rather than dragging and dropping, you can freely experiment on the new copy while the old one remains intact.