A patch was released on October 5 that fixes this issue. Please reach out to customer support if you run into any issues downloading the patch. Thank you for your patience!
It came to our attention that there is a bug affecting Puzzle Quest: The Legend Returns where a skeleton is appearing at level 5000. We are looking into a fix for this now, and in the meantime have found a workaround.
This bug is affecting certain languages, but not English. If you change your Switch system settings (not the game settings as it must by system settings) to English, you should be able to progress. This isn't the language you select in-game, but the one you use for your console.
We are continuing to work on the issue and putting together a patch. Thank you for your patience during this time.