sejuani's E is bugged

Here's the problem : sometimes when I have 4 frost stacks, E just wont activate. The hammer icon is shining blue, Im withing range, I spam the E button, and nothing happens. Sometimes it works fine. It seems random... Here are some examples https://webmshare.com/GGYZ7 Here I'm litteraly smashing the E button for 10 seconds (since the hammer gets blue) and at some points it misteriously works https://webmshare.com/VJ5Jz