Warwick W (Blood Hunt) Sometimes Not Working?

Watch the video. Warwick spawns and there is an enemy Ahri below 50% hp but she is not being Blood Hunted. This happens quite often. Usually when you just respawn, but not always. I don't know if this is intended or not but it says nothing about it in the ability description. It says "Blood Hunt cannot be activated while in combat with a champion" but even in combat you still hear the music, see the blood trails, and see the wolf icon above the enemy. You just lose the MS when in combat.