So the issue is that when another unit is between you and your blood scent targets trail you will lose the speed. This is a bug, but reported for quite some time, unfortunately Riot is doing nothing to fix it or acknowledge it.
Additionally his Q will not latch properly at times, I believe it's due to timing with something like EZ E.
His bonuses are increased by 2.5x instead of 3x
His R indicator randomly increases size as movement speed increases sharply well over his actual limit and lies to the player.
He's got more, but I think you get the point, he's trying to take mordes job.