Attempting to migrate mailboxes from Exchange 2010 to 2016 stalls with StatusDetail: StalledDueToTarget_MailboxCapacityExceeded

Problem

You’re in the process of migrating mailboxes from Exchange 2010 to Exchange 2016 with both a live as well as an archive mailbox and while some mailboxes successfully move to the new databases, you noticed that others remains in Syncing status indefinitely:

Expanding the More Details… option show the synchronization has stalled for quite some time:

Executing the cmdlet Get-MoveRequest | Get-MoveRequestStatstics -Format-Table -AutoSize displays the StatusDetail StalledDueToTarget_MailboxCapacityExceeded:

Executing the cmdlets:

Get-MoveRequest administrator | FL

… or:

Get-MoveRequest | Get-MoveRequestStatistics | FL

… does not provide additional information.

Reviewing the properties of the migration job and clicking on Report: Download the report for this user:

… displays a report with the following log output:

7/2/2017 10:14:11 AM [CONTBMEXMB01] '' created move request.
7/2/2017 10:14:11 AM [CONTBMEXMB01] '' allowed a large amount of data loss when moving the mailbox (50 bad items, 0 large items).
7/2/2017 11:07:56 AM [CONTBMEXMB01] Relinquishing job because of large delays due to unfavorable server health or budget limitations with a request throttling state 'StalledDueToTarget_Processor'.
7/2/2017 11:51:16 AM [CONTBMEXMB01] Relinquishing job because of large delays due to unfavorable server health or budget limitations with a request throttling state 'StalledDueToTarget_Processor'.
7/2/2017 11:15:00 PM [CONTBMEXMB01] '' suspended move request.
7/2/2017 11:15:02 PM [CONTBMEXMB01] Suspending job.
7/2/2017 11:15:02 PM [CONTBMEXMB01] Relinquishing job.
7/3/2017 10:04:41 AM [CONTBMEXMB01] '' resumed move request.
7/3/2017 10:04:45 AM [CONTBMEXMB01] Job resumed with status 'Queued'.
7/3/2017 10:04:45 AM [CONTBMEXMB01] Relinquishing job.

Attempting to log onto the Exchange 2016 server and adjusting the parameters MaxActiveJobsPerSourceMailbox and MaxActiveJobsPerTargetMailbox in the configuration file MSExchangeMailboxReplication.exe.config located in the directory E:\Program Files\Microsoft\Exchange Server\V15\Bin does not correct the issue:

Solution

Attempting to search for the error messages:

StalledDueToTarget_MailboxCapacityExceeded:

… and:

StalledDueToTarget_Processor

… did not return any helpful posts and what ended up being the problem was the archive mailbox server we were using to move the archive mailboxes to.  The server’s CPU utilization wasn’t particularly high (2%), memory usage was average (90%) but the server uptime was 82 days and there were pending Windows patches asking for a reboot. Previous mailboxes that were stalled would successfully completed after the server restart:

Hope this helps anyone who may encounter this issue and unable to find any useful information on the internet.