I hope you meant 17 and not 18
Regardless, I don't believe auto subs are
broken on M16 per se (provided that you set the CFM autosubs as well). The issue is more that a 50 fatigue setting isn't as effective as it should be at getting players to sub out (they were pretty good though before the last patch/tuner). Sure, you can set fatigue higher and they work fine, but doing that has a deleterious effect on the gameplay dynamics (and difficulty) when using default sliders.