Bumping because i have the same problem.
Part of the HOPE IV achievement requires you to kill 3 “ancient” mobs; A veteran fleshreaver, A veteran skelk and the Legendary Karka Queen. However after completing all the prerequisites i was not awarded the Charged Dwarven Spell Trap.
I have attached an screenshot showing my achievement panel. The top row shows my dwarven trap + 3 prerequisites as complete while my mouse hovers over the still incomplete reward.
I have found that both fleshreaver and skelk reward me with the achievement upon killing them, however the Karka Queen rewarded me with an ITEM instead which then proceeded to trigger the reward. I believe this item to be the root cause of the achievement not triggering properly.
