Ash's shuriken does not strip armor sometimes

[Monrka]

When playing as client Ahs's shuriken with augment sometimes does not strip armor from enemies. 

I definetly have enough strength for full strip but sometimes it just doesnt happen. Ability hits the target and adds slash proc but does not strip armor. Also several casts on the same target does not strip armor either - just keep stacking slash procs.

I noticed that it happens most often on Thraxes in Zariman.