I don't really know, but Lox'es seem bugged for me too.
Reducing the distance seem to help, as from my experience when trying to snipe down loxes from afar I often Do hit the target and get zero reaction back.
Once I shoot it from afar and made sure I hit the target, when I came closer to check on Health the lox had full HP bar.
So I try not to shoot at them from great distances. As they will just soak the arrows/bolts and that's all.