Sometimes Warwick's W works and sometimes you're helplessly speeding up and slowing back down even if you're on the trail moving towards a bloodhunted enemy.
I wrote this off as the path changing and the visual just needing a second to update, but alot of the time I would move straight down a lane towards an enemy at 40% HP who, for the record, does have a mark on them and i would move at normal movement speed and speed back up at completely random intervals.
That's not all, however. The Attack speed increase could also use some quality of life changes.
My guess is that it checks on auto attack if you're indeed attacking a bloodhunted enemy, which would make it obvious why sometimes it takes a full animation at normal attack speed to actually increase your attack speed. I don't know this for sure, but it feels that way and it doesn't feel very practical at all.
An example of the ability's weird behaviour would be that you keep the attack speed after you engage a target that isn't bloodhunted for one auto attack if you attack right away after being engaged with a bloodhunted target, which is why, in the first place, I suspected it refreshing on auto attack.
All in all, the entire ability just doesn't feel good in general.
Sorry for my grammar, thanks for reading, I hope some changes will be considered.