Messages Disappearing on Microsoft Teams.

Mark_Kirschenmann 

I have not seen this issue yet. Are you using the desktop client for Teams? If so, are you able to duplicate the issue logging into Teams on the web (teams.Microsoft.com/go)?

If you cannot duplicate the issue using the web version of Teams, I would say there is something going on with your desktop client and you may want to try to clear the cache from Teams. 

1. Exit Microsoft Teams client by right-click on Teams from the icon tray and select Quit, or run Task Manager and select Microsoft Teams, and then select End Task.
2. Open File Explorer and type in %appdata%\Microsoft\Teams.
3. When you are in the directory, you must remove the files in the following folders.

- Application Cache - %appdata%\Microsoft\Teams\Application Cache - Application files, cached CDN files ( JS,CSS, etc ) Locations

- Blob_Storage - %appdata%\Microsoft\Teams\Blob_Storage (If there)

- Cache - %appdata%\Microsoft\Teams\Cache - Web Cache for Electron(Images, JS files, Cookies, Profile Photos)

- Databases - %appdata%\Microsoft\Teams\databases

- GPUCache - %appdata%\Microsoft\Teams\GPUCache

- LocalStorage - %appdata%\Microsoft\Teams\LocalStorage

- Tmp - %appdata%\Microsoft\Teams\tmp

4. Restart the Teams client.

I hope this works out for you.