Aatrox passive bug

So in the past 2 days i have played about 4-5 Aatrox games and i have been seeing a big problem with his passive. For those who dont know his passive is basically a free Guardian Angle after you get it fully stacked, But the problem i have been seeing is that his passive with not stack. Like in my last game i just had with him i got into a fight and my passive stacks would not go past 30% the whole fight, Or another one i got into a fight and i popped my ult, Well on Aatrox's ult it says that for every auto attack hit that it grants 20% to his passive, Well from what i have seen it does not do so. I do not know if i am the only one having said problems with him but i feel that this is something that breaks Aatrox and should be looked into as soon as possible.