Riven unlock quest bugged: "Kill 4 Dargyn Pilots before they hit the ground while sliding"

[dAPico]

Killed roughly 10-15 Dargyns now for the last 1-2 hours, not a single kill counted towards the riven unlock quest.

Approach: Nova (slow build), Lenz bow. Riven itself is a Pistol one.

Please guys, fix it. It's really annoying.

[Krogothar]

You have got to pull them out of the dargyn first then kill them as they are falling.

[Gorden121]

I am also unable to do this quest. It's not like most Riven Challenges aren't actually fun, but just annoying, but this one takes the cake.

A friend has the version without sliding and also cannot get it done. No matter what we do it doesn'r work. 
I even watched a video with the same build and method OP described and while in the video it worked flawlessly it doesn't work anymore. I am doing the exact same thing, the same thing happens as it does in the video but it doesn't work.

Please just delete this challenge. It's not fun and terribly inconsistent.