I have tried everything in the course of six months and this exotic is still unobtainable because of a glitch. I imagine it was because my warlock did majority of the quest and my hunter finished the raid after doing the puzzle. What happened was when I went to loot the second chest was that I received the triumph instead of the gun, and my quest step was no longer available non any of my characters. And as there is no way to repeat this quest, or pick it back up, I cannot obtain this exotic. I’m guessing it’s because for all intents and purposes that the game see my quest as finished and the triumph reads that I obtained it so I should have the gun, but I do not. Below is a link to one of many posts I’ve made about this bug. https://www.bungie.net/en/Forums/Post/255664376?page=0&sort=0&showBanned=0&path=1