I acquired Mountaintop the day before Shadowkeep came out, but it is not in any of my characters' inventories or in the vault. I did not dismantle or infuse it. The gun doesn't even exist within the Grenade Launcher collections, but my Recluce does, for instance. I've completed the quest from Shaxx, and the Triumph has been completed as well. What do I need to do to acquire it again?