There are a few possibilities,
1. Lost in mail somehow. Since the game is new, obscure bug is possible.
2. I simply missed or deleted the delivery mail by mistake, or I just didn't remember correctly.
3. Some member was not sure how the market system work, claimed the work order and checked delivered but didn't deliver in game.
4. Some member was abusing the system. I got 95% plus of my work order filled properly and I always thank guildies who fill my work order with a brief in game mail. That's why I know I probably didn't get the delivery of that particular work order.
I am not sure how to proceed, maybe I can get which Elder to contact here and send a PM?
Missing a delivery is not really a big deal, but in case there is some member abusing the system, I would like to help stopping it.