We have same issue,
I am not sure that this is the right way but it worked for two users, basically users added again their MFA in their ccounts
The user has access her account and "refresh" her login, I mean (View account--> Security Info --> Add sign method.... scanned QR code), the other user did not have access to her account then in Admin Center we removed MFA for a while, then she logged in and "refresh" (added again) her MFA.
After that, reset PC and open Teams, the message again appeared but in the upper right corner was a "Sign in" button, she clicked and message disappeared and user is working fine (chat, video calls, scheduled/record teams were tested)
I hope this will be useful