(Gameplay) Siren Cassiopeia's Miasma can't be seen to the enemy team.

Just played a game against Siren Cassiopeia and whenever she throws her W (Miasma) no one on the enemy team could see the ground effect. Randomly walking into an invisible poisoned ground. It happened once and since I do not own her, we could not reproduce it. We had someone spectate and he could see the purple ground but it was invisible to us.