So if you reverse this, where the first character is following. Does the first character keep on running into the second character slowing down and then resuming. Almost like they have the carrot and the stick trinket, or high speed mount or something?

if you have both characters race each other, numlock down 3...2...1 and you watch them. Does one or the other teleport a bit and then catch up from time to time? I would think you need to reduce your graphic settings to the right most position and see if that helps.

I definitely see this (where the slaves will stop following) with flying mounts and crusader aura if the paladin is leading / being followed until i got a crazy system.