Sejuani spell bugs

I've been playing Sejuani for a couple of games now and I think the "stun stacks" for E is not working properly. First off, as soon as the stacks are full and I want to use my E (E+click enemy), it cancels automatically. Like I have to wait, 1-2 seconds with the enemy fully stacked to actually stun it, and it's a huge disadvantage, this game having split second decisions. And the second bug I've noticed is that, players around me, don't apply the passive, not always, for example in early game, in a 2v1 situation when I gank my ally stacks the passive, but in team fights, almost none of them work, or it's random. Maybe It's just me, I want others to tell me If this is an issue just for me.