Did i find a bug or am i just stupid?

So I was playing blitz supp and the enemys were playing zilean and xayah bot lane in an all in xayah ulted and flashed back i caught up to her pressed e and went for the knock up i auto attacked her and guess what no knock-up and the blue glow around my fists dissapeared as if i did hit her yes i pressed e then instantly hit her there were no minions around zilean was there but he was in tower she didnt have any items to stop the knock-up does zil or xayah have any ability to stop this knock-up?

I am pretty new at league lol not like just started playing yesterday new i have played atleast 200 hours but i am still new enough to not know these things