I know exactly what you are taliking about, but I have no idea what causes it. I have seen the same thing on several different brands of binos. It appears as a narrow solid band on the very edge of the FOV and depending on the light source can look clear and unfocused, and at times may take on a slightly hazy look. It definitely is not veiling glare.
Perhaps Henry can chime in with an opinion on what would cause this.