Kuva Ayanga and killing Dargyn pilots before they hit the ground

[(NSW)Kadet]

Doing a riven challenge, "Kill 5 Dargyn pilots before they hit the ground".  I've noticed the Kuva Ayanga can kill them just fine, but doesn't register on the challenge.  Tried it in both mech mode, as well as a Heavy Weapon on my warframe.  I also tried Proboscis Cernos, its very hard to land the hit, but when you do, the explosion shows 2 sets of affinity numbers (you know it killed both), but doesn't register.

Had to resort to Mesa's aim-bot mode.