Myself and a number of other users are having issues in Outlook.
I have a number of Mailboxes that I have access to in my Outlook - non-user ones that normally several of us monitor.
I find that sometimes (and I haven't found a specific trigger yet) when I go from the Inbox of one mailbox to the Inbox of another, my Outlook gets stuck 'loading' the new Inbox contents, and they never display. A bar at the top of the email list says loading and the orange bar cycles across the section, but no emails ever load. I try click on another mailbox - same thing. It gets stuck.
A possibly related issue - When I try to categorise emails in these other folders, the first time I attempt I get an error: "You don't have appropriate permission to perform this operation". I try again and it works fine. I can then do any others in that mailbox as well. As soon as I move to anoher mailbox and come back again, I get the error again.