Exchange 2013 to 365 minimal hybrid migration

You can try this solution - New move request remains in queued status - Exchange | Microsoft Learn 

Please check teh status of migration.

Get-MoveRequest  | Get-MoveRequestStatistics | Select *TimeStamp, DisplayName, StatusDetail, TotalMailboxSize, TotalArchiveSize, PercentComplete 

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If no progress remove and create new one with a higher bad item limit from powershell.

Interesting this is what I get when I check to status of the migration using the command you provided although I have no idea what it means or how to correct:

Request was quarantined because of following error: ASSERT: AddFolderToProviderMapping(): Folder [len=46,

          data=00000000F06FDE61E13D3842A5E8CC09B5CC84940100264FF09277EAB648AD9CE280E4FC44B20000000001150000] cannot be

          mapped to provider 8. It is already mapped to provider 4

Try remove and create a new move request with a higher baditem limit.

Removed the move request and changed with a higher baditem limit but same result:

 Request was quarantined because of following error: ASSERT: AddFolderToProviderMapping(): Folder [len=46,

          data=00000000F06FDE61E13D3842A5E8CC09B5CC84940100264FF09277EAB648AD9CE280E4FC44B20000000001150000] cannot be

          mapped to provider 8. It is already mapped to provider 4

And the odd thing is when I perform a google search on this error, there are no matching results. One mailbox is holding up the whole process, frustrating.

Noticed the mail box size was 35GB, is that an average size for your other mailboxes?

Hello, no it is one of the higher ones but still under the 50gb limit. I had a couple of mailboxes similar in size that had no issues.

The only other thing I have is has a domain administrator account got full access to that mailbox. When I did my migration, I had to go through all mailbox's and add that permission. Or the mailbox has some corruption that is stopping it.

You can check the following article to apply to this single mailbox and check if any helps:

Stalled due DiskLatency/UnknownReason/ - Resolved

Indeed it looks strange - looks like broken folder structure in this mailbox. Try to fix this mailbox with New-MailboxRepairRequest, than try to export repaired mailbox to pst file.