This is just a shot in the dark, so forgive me if I'm totally off base, but... Is it possible some of the posing and arranging of objects (walls, floors, etc.) were done in frame 30 and that upon reopening the drawing you were in frame 1? I had that happen once. I'd been doing hair/cloth simulations, and then I did some more edits to the scene, adding some walls (boxes) and scaling them and placing them. Save file, exit, come back the next day, and all of my extra items are gone. Well, they were there in frame 1, just not where I could see them. I advanced to frame 30, and everything was fine.