Fiora Ult

I've noticed normal auto attacks don't always seem to proc Fioras ult. I'm auto attacking zed and we exchanging blows, but I've auto attacked him from the same angle 3 times, sadly that angle has the vital from the ult still glowing that lovely pink/purple. I didn't notice it heal me or give me extra damage.

happened before on a Mord player in the same game.