Achievement: not receiving credit Blade Shakuras

Hi there,

Novice achievement hunter going for Blade of Shakuras in the Legacy of the Void Prologue.

The achievement requires the killing of 20 units using Zaratul’s Shadow Strike ability during the Evil Awoken mission. At the mission complete screen, it indicated there were 49 kills with Shadow Strike, yet no credit for the achievement?

Is this a bug or am I missing something? Like should it be 20 “hybrid” units killed?