League of Legends (LoL) Question: Hallowed Mist bug?

I have been finding some people ingame that just ignores the mist, for example: Yesterday i went mid (cause my team partner went top), my lane enemy was a Seraphine, i tought that was going to be an easy matchup, cause sera's a ranged champ, and my mist was going to protect me. But every attack from her hits me, every time. And yes, she was outside the mist, so my question: Is there an item that prevents the mist from working? It was a bug? Thats not the only time, it happens more times with different champs