I may be wrong here, but I noticed when you are farming the exotic class item by doing overthrows in the Pale Heart, the drop rate decreases as you do more. Usually at the start of each week I get ONE for each complete overthrow, but after 5 or 6 drops, it becomes almost none. Similar to the pathfinders and how you have a weekly limit. Like 150 bright dust becomes 30, or Ergo Sum and becomes legendary engrams, when completing pathfinders. Just wanted to put this out there maybe others had the same experience.