After you move a mailbox from the on-premises Microsoft Exchange Server environment to Microsoft Exchange Online in Microsoft Office 365 in a hybrid deployment, you receive the following warning message:
Warning: Target mailbox unlock operation was not replicated. If a lossy failover occurs after the target mailbox was unlocked, the target mailbox could remain inaccessible.
Error details: Mailbox changes failed to replicate. Database ffab4ac8-d471-41a9-8e43-506f3b121bb8 doesn't satisfy the constraint SecondCopy because the commit time 06/30/2015 18:16:47 isn't guaranteed by replication time <Date> <Time>.
A replication delay in the service occurred. This may prevent some post-migration cleanup tasks from taking effect immediately.
The user may be unable to access his or her mailbox immediately after the migration is complete. As soon as replication is complete, the user will be able to access his or her mailbox. If the user continues to be unable to access his or her mailbox 60 minutes after the migration is complete, contact Office 365 Support.