I'm making a new project called Cat World 3, and there's a game called Cat Bounce, which has these little brown treats. I also made a matching game, stopped and saved, everything was fine. I go back into the project and I see a LOT of the card sprites have their costumes turned into the treats from Cat Bounce! I fixed it by naming the costumes, which took FOREVER. THEN, I make a Sand Castle game, making duplicates of the many blocks you can use to make your castle, saved it, went back to see that THEY have ALSO turned into the treats from Cat Bounce!

Note- The file size of this project is a bit large, so that's causing it possibly?

1. You have too many sprites. Try using cloning instead.
2. You have too many costumes of the same name.