I believe it’s the third Human mission, where you have to construct a Shipyard as well as four oil platforms. I had a habit growing up of harvesting all resources (wood/gold/oil) that I could before completing the mission objectives. In this case, it seems that you have to have four oil platforms up and running concurrently instead of being able to, for instance, drain three deposits then build the fourth platform to complete the mission.
Yes, I realize this is wildly overkill/stupid/whatever. But, for the sake of completeness… 