Poppy's ult not dealing damage

Im not sure of the reason, but Poppy's ult isn't dealing damage, at max rank it should do 400dmg +90% bonus ad, but i noticed that it doesn't deal any damage (life of targets unchanged after targeting them), even targets with practically 0 HP have their remaining health unaltered, regardless of how much i charge the ult.

Not sure why, my thought is that the invulnerability effect is kicking in before the damage is dealt.