Migrating mailbox from Exchange Online back to On-Premises (Exchange 2010) - Source user 'John Doe' doesn't have a primary mailbox

I originally migrated a couple users from on-premises Exchange 2010 to Exchange Online/O365. That ended up working somehow.
Now I'm trying to migrate one of the users back until the free/busy stuff is fixed, and it's failing.
The move command is:

Get-RemoteMailbox "John Doe" | New-MoveRequest -OutBound -RemoteTargetDatabase 'STAFF01' -RemoteHostName mail01.domain.com -RemoteCredential (get-Credential) -TargetDeliveryDomain domain.com -Verbose

Then it comes back with the error:

Source user 'John Doe' doesn't have a primary mailbox.

So I check in Exchange, and the AD account John Doe doesn't even show up when I go to create a new mailbox, so I can't try to create a mailbox and match it with the Exchange Online GUID.

But I checked the msExchMailboxGuid attribute for the on-premises user, and it matches the GUID of the corresponding RemoteMailbox GUID.

I tried doing the migration from Exchange Online in the EAC and it says it completes successfully, but it happens in like 5 seconds and really doesn't work. It's a 3GB mailbox and doesn't migrate from what I can see. So it's obviously not working out there.

Should I try manually removing any Exchange related attributes from the on-premises AD user, without removing their AD? Anything else I can try?