I've gone to the Vex Gate located in Sorrow's Harbor as indicated in the video below. According to the source, the quest Divine Fragmentation should drop when I defeat the boss after several waves of Vex.
I have done this several times, and each time the outcome is that the boss only drops a blue engram and nothing more. Is it RNG related? Do I need specific DLC in order to access it? I'm confused why it's not dropping.