During Exchange backup, Veeam Backup for Microsoft 365 requests the properties of all mailbox folders, including the properties of hidden and legacy folders (e.g., ‘TeamsMessagesData’).
Due to a recent change in Microsoft 365, the properties of the ‘TeamsMessagesData’ folder cannot be retrieved using the EWS API, which is used by Veeam Backup for Microsoft 365 to process Exchange data backup.