Microsoft Sudoku has once again lost my progress on daily challenges. Please advise when this issue will be fixed and my progress will be restored.

Excellent! That did the trick and no need to run Xbox before Sudoku. Launching all other games like Solitaire and MUWG automatically create the proper Xbox credentials as well. Thank you so much for posting this!

JulianLong has replied to your question Microsoft Sudoku Access Lost in Microsoft Community.

Just came across a fix that has worked

Go to your userprofile\AppData\Local\Packages\Microsoft.XboxIdentityProvider_cw5n1h2txyewy\AC\TokenBroker

If there are Accounts and Cache folders available delete them. (I renamed them to be on the safe side) But this worked well.
Now try starting Xbox and signing into Sudoku.

This worked for me. Thank you for posting and thanks to JulianLong for posting the fix in your thread.

JulianLong has replied to your question Microsoft Sudoku Access Lost in Microsoft Community.

Just came across a fix that has worked

Go to your userprofile\AppData\Local\Packages\Microsoft.XboxIdentityProvider_cw5n1h2txyewy\AC\TokenBroker

If there are Accounts and Cache folders available delete them. (I renamed them to be on the safe side) But this worked well.
Now try starting Xbox and signing into Sudoku.

I'm having the same issues as everyone else in this thread. Sudoku only allows me to play as a Guest starting over at Level 1. All my previous levels have disappeared.

All other Msoft games (Minesweeper, Solitaire, etc.) work as usual.

I noticed that when I start Sudoku, the Xbox log-in windows pops up briefly and then disappears leaving me as Guest.

I understand this is a "free" game (except for the pain of watching or skipping ads) but I hope this issue is resolved soon.

Here's an update from Feb 2 - I am no longer able to play on my other device. After playing games successfully on it for the past 2 days, this morning the game took several seconds to load and when it finished, I was greeted with this screen which means all progress has been lost:

At least MS is aware of the issue now: https://microsoftcasualgames.zendesk.com/hc/en-us/articles/23365549134100-KNOWN-ISSUE-Sign-In-Issues-in-Microsoft-Sudoku