Solved!
Complete the following steps:
- Open the File Explorer and paste the following into the address bar to go to a specific location on your computer:
- %userprofile%\AppData\Local\Packages\Microsoft.XboxIdentityProvider_8wekyb3d8bbwe\AC\TokenBroker
- Delete any accounts and cache folders that you can see at this location.
- Launch the Xbox App and sign in to your account again.
- Launch Microsoft Sudoku and you're in