Team and Channels continually disappearing from Teams App

Can anyone advise what else we can try to ensure the list of Teams/Channels a user is part of appears in their Teams app list please?

A user is having a recurring problem where Teams are missing from their list.  They are still Members/Owners of those Teams.

We have continually reset the app, cleared the cache, checked the app version, uninstalled and reinstalled the app and the issue resolves for a short period of time and then it comes back again. 

What are we missing?  What can we do to permanently resolve this? Is this a Teams app issue or is it linked to the computer?