If your character is damaged, Arma will set your sway back to 1.0 for some reason. This problem only seems to be a thing since the last update. (1.54)
- Legacy ID
player enableFatigue false;
player enableStamina false;
player allowSprint true;
player setCustomAimCoef 0;
You can see the aim is stable, until your character takes damage. Sway goes back to Arma default.
Demonstration of the problem using A3 Editor: