Occasionally when new email comes in Outlook will not display the message in the main list pane. The navigation pane does indicate there is a new unread message in the inbox however you can't see the message in the main email pane. The only way to see the message is to either click on another folder then click back to the inbox or to change the current view from messages to something else then back to messages. Both work-arounds seem to force the list pane to refresh and show the new messages. No filters are applied to the mailboxes either.
This issue is happening to 2 users in my organization and this seemed to start when I migrated their email from our Exchange 2003 server to our Exchange 2010 server. I have tried deleting their Outlook profile and recreating it but the issue remains. Any suggestions on what to try next?