Kayn ult bug?

I am wondering if anyone else has experienced this. I just unlocked Kayn, and was trying him in a couple of casual games, but I would swear that half of the time, his ult does absolutely zero damage. It doesn't seem consistent. I jumped into an enemy champ with two bars of health left, there were no other allied or enemy champs nearby, and when I exited the champ, their health bar didn't change at all. I believe it happened a second time that game, but that was in the middle of a big fight, so I couldn't tell if someone shielded or healed them in the middle of the chaos. Has anyone else noticed this?