Darth Vader Duels End Level 15 Focused Datacron not granting Bonus Turns

DVDE's FDC states: "Whenever an enemy attacks out of turn, Vader (Duel's End) takes a bonus turn (once per turn)."

I have not been experiencing this at all as of late-- He's just... Not receiving bonus turns, at all, except from the Vengeance mechanic. It most commonly occurs when facing an individual that calls a Mass Assist, but even then it USED to work. 

This most recently almost made me lose a TW Battle, and has been a problem in GAC aswell.