To put it simply, auto-tracking attack is when your character or enemy body reorient themselves automatically towards the center of the target. It behaves like auto lock-on in game like Dark Souls, but auto-tracking only moves the subject while keeping the camera as it is. Then in a game where there's a enemy with multiple hitboxes on a single body, attack from you usually can only register a single hit. Usually there's weapon with ability to register multiple hit on 1 enemy, but usually it have low damage as an offset.
To put them together, auto-tracking attack when you can only register a single hit on 1 enemy leads to accuracy problem. When you want to attack certain body part of your enemy, your character will reorient itself despite your attempt to position and direct the attack accordingly. This lead to the attack register a hit on different spot from your intention. In Horizon, this problem happened to me when I want to take off Sawtooth's blazer protective layer. I stunned the damn thing with tripwire, and out of three heavy attack, only one registered properly on my target while the rest of two landed on its upper thigh armor somehow.
I know that the primary combat of Horizon is ranged, and melee only serve as an emergency measure. However, melee heavy attack that supposedly used to strip armor off an enemy, become annoyance when you want to strip specific armor layer because of the problem above.