If you use Necrotic Grip (or an Exotic Class Item with Spirit of the Necrotic) and use a Melee Ability to kill an enemy, it won't activate Devour, and if you kill it with a single Threaded Needle, it won't create a Tangle. After removing Necrotic Grip, the issue goes away: Melee Abilities now properly active Devour and Threaded Needles create Tangles.