Sejuani's E is bugged [Gameplay}

When i say her E is bugged, what i mean is the fact that if you get all 4 frost stacks on an enemy or even a monster, the frost hammer will be full and my E will be light up. Can mash my E all i want and some times i still wont even go off. This doesn't happen on monsters as often but more likely on enemy champions. There is a blue circle showing the range of the E active, but thing is, is that i could be right next to them mashing my E and they still wont be frozen. There have been so many times where i couldve lived or killed someone if my E went off but it refused to. there are other times where i would hit my E and it took a few hits before it finally does go off. Most of the time E goes off right away though. I'm not sure if the reason why E isnt going off is because im moving or it just simply buggy like that. There was a time where i literally ran around kass in a circle mashing my E until it finally went off. Another time would be running from lee and rakan, both will 4 full frost stacks, hitting my E while they are in range and still doesn't go off...then i died :D