My work chat conversations keep self-deleting. I'll see that I have a message, read it, exit, then come back and the message will be gone. Sometimes the message is gone before I even have a chance to read it. Sometimes the messages will stay for a few days then get wiped. It will also delete my posts before they've been received by anyone but when I type and send again it'll work.
It will happen in some chat groups but not others. I know my coworkers aren't deleting them because when I ask they still have all the messages on their account. I have uninstalled and reinstalled but it has made no difference. I don't have any other teams accounts so I'm not sure if it's just this one or would be others as well.
Use teams.Microsoft.com in a web browser. See if your messages appear. If so then it’s probably a cache issue. Log out and log back into teams and that should clear it. Uninstall reinstall actually doesn’t clear cache if I remember right.