A few days ago, some Teams conversations appeared to disappear unexpectedly. They shouldn't have been affected by the organization's retention policies, and the mobile app seems to show the same missing chats. I haven't been able to verify whether they appear in the web version because browser sign-in says my account doesn't exist. Could this be a Teams caching problem, an organization-specific restriction, or actual message deletion?
3 Answers
It may just be a client or caching issue. Try checking the conversation in Teams through a web browser, and also use chat search with a distinctive word or phrase from the missing conversation. Older chats can sometimes disappear from the normal list without actually being deleted.
The browser sign-in problem is probably a separate issue. An account-not-found message can mean you’re signing into the wrong tenant, using the wrong account type, or being blocked by an access policy. It doesn’t necessarily mean the chats are gone. If administrators have access to eDiscovery, they can check whether the messages still exist; the audit log can also show whether they were actually deleted.
Yes, that’s possible. An administrator may restrict browser access through conditional-access or other security policies. IT would need to confirm the sign-in issue and check the messages from the administrative side.
Some older conversations may no longer appear in the regular chat list simply because they haven’t been used recently. Searching for a memorable phrase can sometimes bring them back. You could also move important chats to Favorites, although that may not permanently prevent visibility issues.

I’m not familiar with eDiscovery. Could the organization simply be blocking access to the web version of Teams?