Vi ult bug??

I was playing Vi and when i ulted, the ult channel but i did not run toward the character but instead i just walk and did not finish doing the ult. They did not have qss or spell shield which was really weird. It was if i was running toward the wall and got stuck there. It happen on red side blue jungle. We were fighting on karthus passive and i ulted Ezreal but vi did not charge to him nor did i get cc down. No slow should slow vi ult down and cannot be stop so i think it a bug?

https://www.youtube.com/watch?v=7uvIKXmKfMc&feature=youtu.be

NOTE: THERE IS NO QSS OR ANY SOURCE THAT CAN CANCEL VI ULT!