PF 13 to PF Online Migration - OnPrem PF cannot remove

Hey team,

Following this article: https://docs.microsoft.com/en-au/exchange/collaboration-exo/public-folders/batch-migration-of-exchange-2013-public-folders

I have completed this migration successfully, and am up to removing PF OnPrem.

When I execute Remove-Mailbox -PublicFolder <Identity> on all but the primary it states:

No active public folder mailboxes were found. This happens when no public folder mailboxes are provisioned or they are
provisioned in 'HoldForMigration' mode. If you're not currently performing a migration, create a public folder mailbox.
    + CategoryInfo          : NotSpecified: (:) [Remove-Mailbox], ObjectNotFoundException
    + FullyQualifiedErrorId : [Server=EX1,RequestId=368a41a2-2f58-4b99-ae38-d403d4ec6192,TimeStamp=15/08/2018 8:32
   :14 AM] [FailureCategory=Cmdlet-ObjectNotFoundException] FC69BCEB,Microsoft.Exchange.Management.RecipientTasks.Rem
  oveMailbox
    + PSComputerName        : ex1.contoso.com.au

Org Config:

[PS] C:\Windows\system32>Get-OrganizationConfig | fl *public*

DefaultPublicFolderAgeLimit                  :
DefaultPublicFolderIssueWarningQuota         : Unlimited
DefaultPublicFolderProhibitPostQuota         : Unlimited
DefaultPublicFolderMaxItemSize               : Unlimited
DefaultPublicFolderDeletedItemRetention      : 365.00:00:00
DefaultPublicFolderMovedItemRetention        : 30.00:00:00
PublicFoldersLockedForMigration              : False
PublicFolderMigrationComplete                : False
PublicFolderMailboxesLockedForNewConnections : True
PublicFolderMailboxesMigrationComplete       : True
PublicFoldersEnabled                         : Remote
PublicComputersDetectionEnabled              : False
RootPublicFolderMailbox                      : 6061b16f-3964-4f2e-8728-714beb1d980d
RemotePublicFolderMailboxes                  : {}

Org Config Root Mailbox:

[PS] C:\Windows\system32>(Get-OrganizationConfig).RootPublicFolderMailbox | fl

IsValid              : True
CanUpdate            : True
HierarchyMailboxGuid : 6061b16f-3964-4f2e-8728-714beb1d980d
LockedForMigration   : False