Poppy Ult Passed Through Target

I was playing Poppy, using the Lollipoppy skin, and once during the game I went to ult the enemy Lee sin as he flashed his mastery 7 emote, and my ult passed through him. When it should have connected, it showed the knockup debuff under his hp bar briefly, then it disappeared as he kept on walking away, not even phased. I attempted recreating this bug with a mastery 7 emote user, but it didn't work. I was not able to try it with a lee sin flashing mastery 7 because I didn't have any friends that have mastery 7 on lee sin. I'm not sure what caused this, but i did get it recorded here in .25x speed.