A5 is purely to tell the archive task what mailboxes to archive next, so what will happen is when the task starts it will put every single enabled mailbox in that queue for that task, and as it processes it , it will remove it.
After the queue has been processed, and if the task is still in schedule, EV will then re populate the A5 queue with any mailboxes that still had items to archive after the 1000 items per pass (unless you're using quota based archiving)
it is safe to pure the queue, you may want to stop the services, purge the queue and then purge the admin queue, otherwise you will get events saying that the queues have been purged for each item.
As for the Update shortcut locations, you should hopefully expect better performance around this area in EV8 SP4.
Also make sure you run regular maintenance as the queries are all very index intensive
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