I got this off facebook:
Hi Sudoku Players! If you are having an issue with losing Daily Challenge or Level progress, our team is aware and currently working on a solution.
If you haven't already, please 'follow' the Sudoku article "I’ve lost daily challenge or level progress”. By following this article, you will receive a notification of any changes or updates, including when a fix has been made: https://microsoftcasualgames.zendesk.com/hc/en-us/articles/360049237871. Thank you for your patience!