More than one ComponentShared mailboxes exist for this user

During what I thought would be a routine mailbox migration from Exchange 2010 to Office 365, some mailboxes refused to move to their new location in Exchange Online. Reviewing the Migration reports for the user, we noticed that there were error messages

John Smith
Data migrated: 1.816 GB ‎(1,950,176,027 bytes)‎ 
Migration rate: 0 B ‎(0 bytes)‎ 
Error: MigrationMRSPermanentException: Error: An error occurred while updating a user object after the move operation. –> More than one ComponentShared mailboxes exist for this user. To prevent Primary mailbox from coexisting with ComponentShared mailbox, this MailUser cannot be converted into a Mailbox. 

The error message is a bit odd and somewhat unclear as to what is the cause of the error itself. What is a ‘ComponentShared Mailbox’? What does the error message mean that there is more than one ‘ComponentShared mailbox’?

Get-Mailbox | ft MailboxLocations

Normally, you would see something like this, where the word ‘Primary’ is shown in the results for the MailboxLocations property for the mailbox:

componentshared-01

When you get the error messages shown above, the below results would be expected:

componentshared-02

Notice that the words ‘ComponentShared’ are shown instead of ‘Primary’.

Fixing the Problem
In order to resolve this issue, we need to remove the user from Azure AD and then resynchronize their AD User object back up to Azure AD. How do we do this?
Remove User in Office 365

remove-msoluser -userprincipalname <username@domain.com> 
remove-msoluser -userprincipalname <username@domain.com> -RemoveFromRecycleBin

Once the user is removed, wait 15 min and then run a Directory Sync from your Azure AD Connect server:

Start-ADSyncSyncCycle -PolicyType Delta

Then the user should show in Office 365 and its Mailbox locations should be good once more.

Notes
What is interesting is that if your mailbox has an archive, this is listed in Mailbox Locations as well:

componentshared-03

The original issue I had occurred in September of last year and it happened again in October (various TechNet Forum issues) where Microsoft released a fix for the issue. This article may be just for educational purposes at this time.

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