Can’t see members in Teams group

Tchess 

Try clearing cache and credential manager cache by following steps:

1.   Fully exit the Microsoft Teams desktop client. To do this, either right click Teams from the Icon Tray and select ‘Quit’, or run Task Manager and fully kill the process.
2.   Go to File Explorer, and type in %appdata%\Microsoft\teams.
3.   Once in the directory, you’ll see a few of the following folders:

1. a.  From within ‘Application Cache’, go to Cache and delete any of the files in the Cache location.

    *   %appdata%\Microsoft\teams\application cache\cache

1. b.  From within ‘Blob_storage’, delete any files that are located in here if any.

    *   %appdata%\Microsoft\teams\blob_storage

1. c.  From within ‘Cache’, delete all files.

    *   %appdata%\Microsoft\teams\Cache                                           

1. d.  From within ‘databases’, delete all files.

    *   %appdata%\Microsoft\teams\databases

1. e.  From within ‘GPUCache’, delete all files.

    *   %appdata%\Microsoft\teams\GPUcache

1. f.  From within ‘IndexedDB’, delete the .db file.

    *   %appdata%\Microsoft\teams\IndexedDB

1. g.  From within ‘Local Storage’, delete all files.

    *   %appdata%\Microsoft\teams\Local Storage

1. h.  Lastly, from within ‘tmp’, delete any file.

    *   %appdata%\Microsoft\teams\tmp

For credential manager
Go to path - Control Panel\User Accounts\Credential Manager 
And clear Microsoft's credentials

Hope this will solve the issue.