I'm aware that if you have an Exotic Cipher in your inventory, if you claim the Xenology quest it will be lost. I also believe if you still have a cipher (even in your current or past season pass) the quest also won't be available. But I've heard that if you abandon the quest, sometimes the only way to pick it back up is to delete and start a new character. No quests are in the abandoned kiosk, nor are any ciphers to be found and it's going on months now without the quest from Xur. I believe that this has been an issue for many other players but I don't see it listed as a known bug. Please comment and upvote so Bungie can fix this!