As you can check from the video (timestamp 0:10), my ult was going REALLY FAST on ornn, which made it really hard to hit.
It was a local only bug (other clients saw it going at the right speed).
I don't know how to reproduce the bug honestly, check the video.
We still won the game so it's alright.
Sorry for being french xD
Match Details: https://matchhistory.euw.leagueoflegends.com/en/#match-details/EUW1/4269560628/23522157?tab=overview
Type of Bug: In-game