Strange architecture. They clearly have a queue, but instead of checking previous request, they create a new one. It's like they managed to get the worst of pub/sub and task queue.
No, not that kind of queue. I believe the queue in question is simply the in-memory queue of HTTP requests being processed on each instance, it's neither persisted nor shared between instances.
If an instance is stuck and not replying in time, you make a retry and the new request hopefully will be dispatched to another instance.
If an instance is stuck and not replying in time, you make a retry and the new request hopefully will be dispatched to another instance.