1. I encountered this issue on XBOX AND PC
2. I was playing ALONE
3. I was playing as ALL CHARACTERS
4. The achievement don't properly unlock after killing the different kind of Elite Trolls
Finished my fourth run, one with each character, and still no achievement. Did the maps in this order to kill the necessary trolls:
Designs of the Duergar - Elite Acid Troll guaranteed in one of objectives maybe get a Elite Red Troll too.
Floating City - Red and Green Trolls, almost every time one of both types spawned as elite.
Ghosts of the Past - The Collector.
Finished every map on easiest while hunting for the first 3 troll types, leaving the collector for last as this optional boss is the only Ice Troll that appears as an Elite in the whole game.
The achievement don't unlock.
Unlock the achievement.
I killed all of these with several characters, including one played only offline, as well as stonegrinder, and did not unlock the achievement either. Not sure what is going on with it, but it is not right. I am on PS5.