As far as i have experienced this effect in my image before, moving the fog or haze sliders back and forward, different heights or whatever for the fog, the line never disappeared, only when the fog was totally turned off, logically.
Only with this movement i've described, as odd as it appears, the strong fog line, which bothered me too, vanished - no explanation what should be the difference compared to the slider settings.
But - like i've said, it probably only works on certain settings/atmospheres ...

Well, i hope you'll find a solution for this soon.