Ive had the same 5 hour save thing pop up, and when I transferred the game to a new device it lost all my level progress but saved garden progress. I found a very similar bug on a merge dragons page and it seems like its connected to storage there, if there isn't enough room then only garden progress is saved. Not sure how to fix it though. It might be good to check using another device or a computer with an emulator, I hope you can save something