Additional team and channel-related features and issues within Microsoft Teams for business
Hi Naomi,
If all Teams and messages are visible in the Teams desktop application but most of them are missing from the Teams web client, the content itself is likely still available. This points more toward an issue with the web client, browser session, or Teams service.
I recommend trying these steps:
Sign out of Teams on the web and sign in again.
Open Teams in an InPrivate/Incognito browser window.
Try Teams in another supported browser.
Clear the browser cache and cookies for Teams.
If the issue continues across different browsers, ask your Microsoft 365 administrator to check Microsoft 365 Service Health for any current Teams incidents.
The administrator can also verify that your Teams policies and account permissions have not changed.
Because the desktop application still shows the teams and messages, I would not delete or recreate any teams or channels while troubleshooting the web-client issue.
If the problem occurs in multiple browsers and for the same user consistently, collecting the Teams web client version, browser version, and approximate time when the issue occurred would also be useful when contacting Microsoft Support.