Evil Kraig F (8/29/2014)
Anybody with a solid level of experience in Service Broker able to help someone out? He's new to the site but he's definitely providing what we need and is competent. It's an intriguing puzzle, but I just don't have time to dig that deeply into it immediately.
I weighed in on it. It's a feature of the RECEIVE command, it only grabs the first conversation_handle, not just the first 1000 messages. You can alter it by using a WHERE clause, but it might still simply grab the first conversation each loop. I ran into this a while back when I had a queue of over 1 million messages. It would sit and process 30 messages at a time instead of the 500 that performance monitoring said was the most efficient.