I've had this issue for several months. Error 800 and disappearance of houses, at the moment in the neighborhood of Oasis Springs.
By the way I play, I like to use all the households and go rotating. Sometimes I play with a family and sometimes with others. All the houses edited by me like the sims, with cc.
Obviously my savegame is very big, which I do not care, because what matters to me is to be able to play my way.
I have not played for some time, because I am not ready to start a new game, not even saving families, knowing that I will lose all relationships and genealogical trees. I also know that by the way I play, I will end up at the same point.
What I would like to know is if at some point it is thought to solve this bug, because if it is not, I will probably leave the game forever.