Help with Office 365 shared mailboxes on Outlook 2011 (Mac)

We are migrating to Office 365 and have a number of users and shared mailboxes already migrated. Windows and OWA users are able to add shared mailboxes without issue, however many of our Mac users running Outlook 2011 can go through the process of adding them without error, however they simply do not appear.

The same users are able to access the shared mailboxes using OWA so I ruled out a permissions issue. I have also removed and re-added the shared mailboxes however they still do not appear.

Any ideas on what to check?