There are a few reasons why you may have lost access to a team or channel within Microsoft Teams
Your access to Teams is directly connected with your University affiliations. If there is a change to your status as an active student or employee, you will lose access to Teams as a result.
If you have lost access to a team or channel, please contact one of the team owners to verify your permissions for accessing the team have not changed. If the current owner is no longer available, the team may have expired.
The team, channel, or even some of the files may have been accidentally deleted by an owner or member of the team.
Each team that is created in Microsoft Teams has an underlying Office 365 Group that gets created for managing team membership. Office365 Groups are set to expire every 365 days. At 30 days, 15 days, and 1 day prior to the group expiration, the owner of the team will receive email notifications regarding the pending expiration with an option to renew the team for another 365 days. If a group reaches its expiration and has not been renewed by an owner, the associated team will no longer be accessible to owners or members of the team. The expired group and associated team will still be held for 30 days for an administrator to recover. Open an Incident as soon as possible to prevent permanent data loss.