I thought I had saved the game when I played the game before, but the save data is gone when I start the game again. Is it broken?

There is a possibility that the backup data is corrupted.

If the backup data is corrupted, the system will try to restore it, but if it cannot be restored, the corrupted data will be automatically deleted and the game is restarted. In that case, the data that had been saved up until then will be deleted.