I have migrated from 2010 to 2013 and are having an issue with MailPublicFolders , when a user adds the Public Folder to their Outlook Favorites, new mail disappears after a few seconds. When looking at the Public Folder in Folder view, the mail is visible.
I have found this behaviour is only when using Outlook Cached mode, it works as expected in online mode. There are messages in Sync Issues saying "The following message could not be downloaded (0x8000ffff)"