I noticed that during several fights either one of my characters or a random enemy gets 6 AP at the start of the fight.
They have not saved up AP or any talent, they just sometimes get to start with 6 AP for no apparent reason. Usually after a reload, the game behaves like normal.
Lastly, is Karon supposed to have no armor ? IIRC he had armor in the vanilla version. Makes the fight somewhat easy.