Hello,
make sure there's nothing around reflecting IR. I had the same problem when i mounted a PTZ 25x 4Mpixel camera near a wall. The wall reflected the IR back in a side of the camera dome, making the images foggy.
I Know it's an old thread, but i've exactly the same issue with the DS-2CD2H85FWD-IZS. Mine is indoor mounted.
It's clearly a fault in this camera, because i've many many other type of cameras and i don't ever had such as issue.