Hi,
I have never experienced this problem and don't have the dine out expansion pack but I heard that it happens in cats and dogs as well. You mentioned that it asked you if you wanted to return to normal mode, maybe by clicking yes you relinquished ownership of the restaurant because you disabled the expansion pack. You should try closing the restaurant, moving something again and pressing no to see what happens, if there is no way to move something and still have your restaurant then try inviting the sim over to the restaurant and fixing it there.
I hope this helped, if you need any further assistance please post a video or more detail in this disscussion
