Sion Q slowly losing knock-up

I don't have much information on this bug as I haven't had a chance to try and recreate it yet, but I just thought I'd report it since it happened after playing Sion only once. I just got out of my first match playing the new Sion and noticed issues with the knock-up on his q.

Right off the bat, it wouldn't knock-up when my target was at the edge of the ability. If I fully charged my q and it hit an opponent on the edge of it, it would still do damage but wouldn't knock up. As the game went on, I noticed it working less and less. It would start not knocking up even when my target was right in front of me. Eventually by the end of the game, it just wasn't knocking up at all anymore.

At the end of the game I was ensuring that I charged up my q until the entire range was achieved, so it definitely wasn't an issue with it not being charged long enough. And the ability was still doing damage, so it wasn't getting cancelled either, it was just as if the knock-up part of the ability didn't exist.