I've got an issue as well. I saved my model to my usb, it said my usb was full at first so I deleted some files and saved again. When I open the file later on, it opens to my floorplan view and I am missing walls and windows. What doesnt make sense is when I preview the file before opening, it shows everything there. I tried looking at visibility options but nothing worked. Has this happened to anyone? Makes me want to make back ups every few hours just in case.