Viktor Ult Bug

Just played a game and had multiple cases where my Ult wouldn't follow Champions, even if they were marked as following. I've casted it on them, it follows for a few seconds then randomly stops and the mark disappears. Even if I re-use it on them and the mark returns, it just sits there and doesn't move at all. This happened while I was alive the entire time and when I'd died after placing it, though it's supposed to continue following even after death. No I do not have evidence.