[GAMEPLAY] Udyr Stun Not Always Working

On Udyr, when you are in bear stance sometimes you cannot stun a target, costing you valuable time that could mean either life or death in game. And no I have not bear stanced them prior to this so there isn't the debuff preventing me from stunning them, it doesn't even do damage and i know for a fact i'm not cancelling my attacks either.

https://www.youtube.com/watch?v=Gn8bKVDpsQ8 Notice how i'll attack in bear stance, it does nothing then attack again and it stuns.

Seems to happen when I walk up to an enemy and hit bear stance right before i attack someone and seems like it has something to do with bushes on the map. I attempt to attack but the Stun won't work on first hit, making me have to attack in bear stance a second time, wasting some potential DPS. I've tried this over many games and this has happened randomly throughout them.