It might be caused by how the characters move forward while doing those moves. For instance, I know on wake up I can not teleport uppercut either characters if they are doing those moves since it will whiff.
maybe its a really small hitbox and only hits on the persons current spot and a little in front of them. Both those moves require slight backwards movement maybe it puts them out of the hitbox? I know it doesn't hit people in the air. Even small hops, like Sonya's MS 4 has had me hop over it.
It moves said characters hurtbox when those moves are used. I can't say for Kenshi, but Kabals Buzzsaw makes a lot of specials whiff when they shouldn't.