Cassiopeia's ult does not stun when enemies are facing her

I played a game with Cass today - right after the rotation change. It happened in 3 times (from about 5) when I hit an enemy with my ult and said enemy was facing me. The enemy got some HP taken and only got a mild slow, not a stun as it should have been. I'd gladly send a replay or something, but I am no streamer and have not recorded the match, so I have no video-proof of this.