The requestor ID starts with a B so that means it is a batch requestor or agent that has the lock. How is the queue item created? Are there other agents or batch processes that would be processing the item?
If you have the 'Auto queue management' option checked for the standard agents then I would not expect them to interfere with each other. How is the queue item being created? If you are using Queue-For-Agent in an activity, there is a 'Deferred' option that can be used so the queue item is not created until the next commit. This can help prevent scenarios where the queue item is committed before the processing is complete on the work object. This could apply if you are creating the queue item from another agent process and the the MinimumAgeforProcessing is set to such a value that the queue item could be picked up right away.
The minimum age for processing determines when it should be picked up and processed. Once it has reached that date/time, then the agent should process the item. If there were a failure processing the item, then it would go to the broken queue.