Sorry you're having this issue :/ I can't really say what's going wrong without knowing a bit more about your project. Did you place a player start position on those levels? Are you using any scripts?
Yes, I have placed a player position, but I don't use any scripts. The weird thing is that it doesn't happen until I put entities in there. I don't know if it says anything, but sometimes it happens to me that when I place a new wall on the map, it has a different texture than it should be.