I believe this is because somebody else already damaged that mob, and that you can only loot the items from mobs you kill.
No, because these are monsters that respawned freshly if you look at bottom right corner, it says This item is unavailable for pick-up, which is a similar message to picking up one-of-a-kind quest item like Zakum certificate something is wrong here
Not sure then, and no idea how to replicate this issue. If this happens again please let us know. Also interested to know if the bugged items disappear if you leave and re-enter the map.
I think I managed to replicate the bug. If you are in a party, kill a mob, and get a drop, you will be unable to pick up the drop if you leave the party. If you rejoin the party, you can loot it again, but if the party is disbanded and reformed, the item will be permanently unable to be picked up (I assume because the party id or however it works changes) This happens even with 1 person parties. I originally found this when hunting for the etc for the ring quests, it seems that and the hp quest are both affected by this.
