Dr Mundo invisble cleavers

I encountered a mundo around mid game when he roamed mid, he started throwing Qs and they hit me but were invisible, like I couldn't see them at al. I thought maybe i wasn't paying attention so I didn't think much of it but later on, before a teamfight, he threw more Qs and slowed our adc, who got caught because of the slow and we lost the fight completely, I asked my team and they said they couldn't see the cleavers either, we ended up losing the game because of how we didnt see the slow coming, got slowed, then caught out by the rest of the enemy team.