One possible cause is floor finishes, ie. carpet, vinyl etc.. When a room is created, it fills the space between the floor level that it is created on and a ceiling . If a new floor is added, which is what a floor finish is, and that floor(the carpet) is set a few mm above the structural floor the room will hide between the two floors. The Architect needs to ensure that all their floor finishes have the correct offset from the structural floors with NO gaps.If they do this the rooms and tags should return their correct location.