Last week, the solution for us finally came down from heaven in the form of a gentleman named Anthony at AC level 3 support....
In my case, all it took was an SQL script to remove all Deleted Mailbox items (around 63,000 or so), and everything is back to working beautifully! Kudos to Anthony!
Obviously, I am not sure if this would be the solution for you, but I wanted to put it out there, since I know from the UB that many have been suffering from a variety of annoying and debilitating exceptions/errors....
Good luck,
