still parry issue

Oneoften

Is it normal that in one fight I give parry with stun twice and when I do it in thirt time he will not get stun? In AW it was really amazing see something the same, and the same happend to me in aq when I went to gwenpool in white magneto map, second part, first line, I tahe her with rogue and few times I get her stun and then nothing, just parry without stun...