I started with one family which I split up twice so the members live in 3 different houses. From the initial house, 1 sim has disappeared. From the second house the entire household has disappeared. The third house is fine, which is the most recent one played.
By disappeared I mean in the first house the missing sim's icon is gone, and he is unplayable. In the second house the whole family's icons are gone, but you can still see the household name and funds. When I try to play them the game attempts to zoom into the household but just freezes on the map view. When other sims visit the second house it says "nobody is home".
It's super annoying because the family in the third house have lost brothers, cousins and nieces. The majority of their family has disappeared off the face of the earth.