Azure alert only fired once
A metric alert that's in a "Fired" state would not trigger again until it's resolved. This is done to reduce noise. Resolution happens automatically after 3 healthy evaluations of your condition (evaluations where the condition isn't breached), and there's no way to manually change the monitor condition to "Resolved".
Can you please confirm if you are sending a metric value on every evaluation of the poison queue, even if the value is 0?