I've had the same issue for about a month after I had to perform a reinstall.
In account/linked devices it shows my old computer name and it can't be removed.
The devices list on the Microsoft account page doesnt show my PC, phone or controller anymore. Its either completely blank or I get some strange error string on the website if I try to remove my old device from Windows/accounts/linked devices.
I created a new outlook address and then a new Microsoft account in order to create a temporary new Windows account and my current computer at least shows up and "find my devices" works.
It would appear to be an issue with my primary email address since the reinstall. But seen as so many people are having the same problem on here, it would also suggest that whatever this problem is, it is systemic.
I created a thread looking for help but the lady that was helping me, hasn't got back to me for a couple of days. Going by other people's comments here, there doesn'tappear to be any point in doing a live chat with support either.
So can you do us all the courtesy of telling us all exactly what this problem is (we know that you know) and tell us how to fix it or if we have to wait for a patch.
Thank you.