Yas not being able to aa when fighting riven?

I just went against riven top lane. After she stunned me and her stuns were gone i couldnt aa her. no this wasnt because i was stunned. No i wasnt stuck in the air. I just stood there and wouldnt aa. I moved and was moving fine but would just not aa her. Lost the game because of this. Ive had this happen a lot with champs where the aa wont go of after they cast an ability. I know that there are animation glitches and canceling that can be done ( which this riven abused to the fullest) but idk why when i jump on someone with yas or yi or xin that i just stop attacking outright and cant seem to attack again. Please look into this riot.