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Veeam Backup for Microsoft 365 uses officially supported methods to back up Exchange Online data, specifically using EWS API's SyncFolderItems to identify changed items. As such, Veeam Backup for Microsoft 365 is affected by these internal changes made by Microsoft's maintenance. The problem described in this article relates to internal changes on the Microsoft side that triggered: An item to be resynced via the EWS SyncFolderItems API, which is the standard way to perform backup operations. An item to have a new LastModifiedDateTime, as this can change for any Exchange item that has its internal properties modified. Note: Veeam Backup for Microsoft 365 does not use the LastModifiedTime or ChangeKey as a primary indicator of change but can use them as a secondary indicator to avoid duplicate items with the same values when storing data for backup purposes. Microsoft has said they have made the necessary fixes to prevent unexpected sync events going forward.