What I said is that polls every second. What you asked is how to make it do that. My reply was that you don’t need to do anything to make it do that, and you cannot stop it from doing that. That is what makes your symptom strange.
Unfortunately you have a symptom that should be obvious to every queue user, but no-one else sees. All I can suggest is creating a very simple model, using 1.8.7.x and trying to reproduce the problem on that. If you can reproduce it on a simple model, try and understand what is unusual about that model, and submit a bug report, with maximum debugging turned on for app_queue.
I’m not sure how much debugging is available in app_queue.c, but turning it on your actual system may give a clue as to the problem. I doubt many here would want to trawl through a lot of logs, though.
Funnies with queues tend to happen if you have multiple queues sharing multiple agents, but none should result in entries getting stuck until another entry is added.