I don't have the AF100, but I have seen this on other cameras. I've seen it when the ND filter is between settings (the little switch isn't completely registered in one of the settings). I've also seen then due to high humidity, like going from an AC room to a hot, humid outdoors.
Yeah I already tried moving and fiddling with the ND filter wheel with no luck.
It's also been in cool AC'ed rooms all day. But I'll write back if it goes away with what seems like humidity conditions.