I was invited to group by someone who had Unmaker's Hoard. They had already collected the armour pieces but not killed the boss. They shared the quest with me and I was unable to collect all of the pieces, getting stuck on 3/4. The last item would be visible with a quest marker and my character would go through the kneeling and picking up animation but the quest objective would not update. I dropped quest and they shared a couple more times and as a test I tried collecting the pieces in a different order, but same problem. Finally I dropped quest, they shared again, and I left the group. Once I had done that I was able to pick up all the pieces and complete the quest properly.
PC NA, CP2200+. Character creation is the true endgame.