I have seen several occasions recently where I am getting 2-3 instances in a row of the same archiving task starting processing (event 3156). These all occur within a minute. This results in every mailbox being added to the A5 queue 2-3 times. Each occurance is with the same server and I have already tried deleting and recreating the task.
Since our EV infrastructure is already running full out during the mailbox archiving window, it can't get to the additional items in queue.
Here's the actual event. It occurred three times for the same server within 1 minute and 4 seconds last night. Some nights it starts twice and others only once. Other mailbox archiving tasks on the same EV server only seem to start once, but this Exchange server has by far the most mailboxes.