Lissandra Ult Not Working?

I was playing Lissandra recently and I was in a 1 v 1 with a Shen, I ulted myself and was still being attacked, even if i had ulted him there would have been nothing to hit me as i died right before the ult ended, i took a half of my health in damage while in ult

does shen somehow cancel it? if not it's very strange because it seems as if my own ult was doing damage to me too