Mailbox Move to Exchange Online – Error: ASSERT: Reservation to update is not found

So I came across this “challenge” when trying to move a user from Exchange 2010 SP3 to Exchange Online.

All the others users in the batch worked fine, but one user would get to around 50% and then fail!

The batch log contained:

09/11/2017 17:42:55 [HE1PR04MB2985] User xx.xx' failed migration: Error: ASSERT: Reservation to update is not found

The user log wasn’t much better with:

09/11/2017 17:38:47 [HE1PR04MB3241] Fatal error ExAssertException has occurred.

and

MigrationMRSPermanentException: Error: ASSERT: Reservation to update is not found

So I tried something that I have done before. Using PowerShell and connecting to EXO, I ran:

Set-MoveRequest -Identity xx.xx -SkipMoving: FolderRestrictions, KnownCorruptions, FolderViews

I then restarted the batch

Start-MigrationBatch "yy_yy" -Verbose

And BOOM! it worked. Not sure what the hell was going on but hey, the user moved!

Hope this helps someone ;-)