Is it just me or does it look like the lance is not hitting the mark but the game still registers it quite often? Is it lag or hitbox issue or my eyes just screwing with me? 
The lance doesn't stick in the target, so it hits and as you move the lance moves and a split second after it's hit the target it's away from the target again creating an illusion of faulty hit boxes.
This illusion also counts for the "omg my lance went through him and didnt kill!" you hit an inch to the left of the enemy, and as you ride to the right the lances follows and it LOOKS as if its hit the enemy, but in reality its just the shaft following you as you turn from the enemy, your lance behind him where it missed following you.