Seismic Cry not stunning primed enemies when socketed in Ferocious Roar.

I have been playing a seismic cry bear for a bit into the 90s and I always got the feeling it was dropping the ball sometimes when roaring and not actually stunning primed enemies.

I finally caught it in action when I was recording my Atziri fight.

During the 2nd phase I prime Atziri for stun, and then I use ferocious roar which I have socketed with seismic cry - she does not become stunned.

After I slam she is still primed, and I immediately roar again, burning another endurance charge - still no stun.

I then use furious slam one more time, and the damage from the slam finally stuns her.

You can see it ~1:27 into the fight here.

https://youtu.be/RLvWSLYVRPU?si=K3vvbgCOqFE5awqe&t=86