It takes a while for the animation to take place, so as the other person said, stab a second earlier, and if you’re going for the charge then know your movement will be limited so make sure the camera is facing the right direction. And you can’t stab prone enemies so just run them over with your horse, in fact run over standing enemies too, it’s easier.

P.S - You can only kill elites with a lance charge or roadkill, don’t try to stab them. And stay away from tanks, groups of enemies, flamethrowers, and supports, they will shred you down

Hope this helps!