There is a simple workaround to synchronize the save in cloud:
- Do your daily challenge on pc, click done when finished.
- Open microsoft sudoku on a device (android or ios) with same login and begin a challenge (then exit)
- Click on your Level / Login name in Microsoft Sudoku on the PC (it will open the Xbox app) and when you return to microsoft sudoku it will say it's not synchronized and will do the trick.