There is no houses on the plots

None of the families I try to play with have a house on their lot, there is just an empty space. I don't use any mods. I even tried building a new house using the "motherlode" code, but this code doesn't work either. I saw that players are having a problem with the roof being missing(I’ve experienced that too), but in my case, the entire building is gone. I also tried moving my family to another house, but then I get an error. Some houses have already disappeared from the map, and others are still shown on the map but are missing once the game loads. What should I do?

• missing buildings,
• missing roof,
• extended loading time,
• error 801,