ISSUE: Mailbox Move fails with error 'SourceMailboxAlreadyBeingMovedPermanentException'

Overview

The mailbox move step fails with the error below:

0 % complete. Status is Failed and Status Detail is FailedOther (BadItemsEncountered: 1). Failure message is SourceMailboxAlreadyBeingMovedPermanentException

The root cause is unknown. 

Solution

The customer moved the exchange on-prem mailbox databases which cleared up the issue.  

The user will need to be un-mapped and re-mapped.