Achievements for everything except XBox 360 games keep dropping to zero in all achievements

Off and on for the last few weeks my gamerscore for everything except XBox 360 games shows zero when I view all achievements.

Even though I have completed the achievements for almost every game I have.

When this happens no achievements unlock.

And, frustratingly, this can happen mid-game. I.e. all achievements are showing, i start playing a game and achievements are unlocking and then they stop unlocking, i check all achievements and they've all gone to zero while I was playing.

I have tried numerous ways to fix this - deleting my profile and re-adding it, restarting, completely resetting the console, etc

I thought it might be my xbox one console as it was getting old, so I brought forward my timeline and upgraded to an Xbox X series 3 days ago.

Exactly the same thing is happening on the brand new Xbox X console.

Has anyone had similar issues, and is there anything I can do about this?

Thanks

:)