Queue Trigger - second Queue Item not being processed

I set up a Queue Trigger for my process. It doesn’t work when an item is added to the Queue while a Job is currently running. I would expect it to trigger a second Job as Pending, but it doesn’t. The item added while the Job is already running never gets processed.

So this is strange. The second item did finally process, but there was a 20+ minute delay between when the first Job was done and when the second Job triggered.

What would cause this delay?