When I encounter bandits, and I am on my horse, I kite them (kinda in circle) on my horse with my bow, at some point they stop trying to catch me, they just stand still even if i am few meter away from them in their line of sight, they sheath their weapons ( is like I disappeared) an I can shoot at them, then they start again either fleeing or running back toward me. is like they loose their agro toward me if I run too much in circle.
I noted this issue in a different post, I also ran into this. Basically I think its trying to simulate one of two things, either the bandit reaching the end of his tether zone from the camp or running out of stamina and giving up. It is kind of strange though as you can easily dismount then initiate combat without him reacting, Im sure its a bug with the AI of some sort.