I'm trying to figure out if this is a problem from the
1st point or
2d. The bug you mentioned also reproducing when you go upstairs and down? If yes is suppose to be vanishing mechanics, when some items on another floor hiding to save FPS. But it should't work like that in a Large houses. The problem SE knows described
here, but it can be different case than yours.
I suggest to write about it to their
support center. (
not the forums, forums support are useless)
Im already wrote them about first problem, but can't make a second ticket because have no large house by myself. The house I found(where the case is reproduced) most likely made with 3d party programs, I don't want problems for its owner ^_^'