Cassiopeia Bug

I was in a game last night (5v5 Summoner's Rift) as High Noon Yasuo and facing a Mythic Cassiopeia in Mid. When she would cast her W, Miasma, the pool would not appear on the ground. Minions and I could still walk through it and I could still take damage/be slowed, but I couldn't see it. My fiancee was playing as well, and said she could see it. So she started using the pings on the spots where Cassiopeia cast her Miasma so I could avoid it.