Played a game of ARAM on Howling Abyss. Myself and my two friends experienced the same bug Cass' W Slowing poison was completely invisible. You could walk through it and be poisoned and slowed, but you could not see the pool on the ground.
Same thing just happened to me. Three of us could not see enemy Cassiopeia W on ARAM
Cassiopeia's W is not showing up on the Howling Abyss Map. The ability would slow but not be visible. 
had this happen yesterday with varus slow also, could not see it but i watched him fling it and i was slowed.
just finished a game of ARAM (howling abyss). enemy Cassiopeia had invisible poison, the one that pools on the ground (the W?) anyway, our whole team couldn't see it the entire game, but we were definitely affected by them. It's worse than Teemo's shrooms b/c we can never see them. I see this has been a problem for quite some time. Please fix this, thanks!
I've had this happen for a couple months now and it is consistently getting me killed. Not being able to see a slow right in front of you is a big issue. Need it fixed.
What a sucky bug.... I'm assuming it's an ARAM only thing since I just played a game and had the same thing happen. Not fun at all for sure. Invisible, expanding pool of slowing poison.... GG fed Cass?
27th of March. Just played an Aram. You could see the purple spray but not the lingering cloud of poison.
