Watchstone not dropped by Drox

Hi. Not sure if this is correct place for this post. If not, please inform me and move appropriately.

I am awakening 5 in atlas. I failed to kill Sirus a few days ago. I was told that I would have to rechase down the 4 conquers in order to spawn him again and try again.

I just chased down and killed Drox. He dropped the usual armor/weapon but no watchstone. I cycled thru every loot filter setting just to make sure it wasn't glitched in that regard. I also held L3 to see all leftover items not looted. Nothing. No watchstone.

Please advise. I have the other 3 conquerors ready to go and well, but it's moot if no watchstones drop.

Edit: nevermind. FB group just informed me that I have to kill him in a region which I have not killed him previously in order to get another watchstone. I REALLY wish PoE had optional in game tutorials. SMH