Shadow Nexus

I've been trying to get Hero Armor pieces from this challenge mission. I did the challenge for about 2 hours and got 3 pieces of armor, and after that I've done the mission for about 5 hours (on and off) and not one piece has been placed in my inventory. I was told defeating the Portal Mages would randomly cause an armor piece to be placed in your inventory after the mission, but I almost always reach 100 points and kill at least 7 of the portal mages. Anyone know what the requirements are for the armor pieces and what I am missing? I asked GW directly but they literally would not even try to help.

Thanks.

they are random, and it is after killing portal mages as you've been told.

shadow nexus, in my experience, takes longer than other challenges to get an armor piece.

very frustrating to go several rounds and not get a single drop.