Hoya ND400 filter quality

I got 2 Hoya ND400 filters (9 stop ND) for my cameras, 57mm for Fuji 14 mm WA and 67mm for Nikon 85mm and soon coming Sigma 35mm.

I did some test shots with Fujifilm X-E1 and the said lens/filter combination. I noticed there is a curving vertical area in the left side of the picture which is soft, looks like bad contrast softness. It becomes worse when stopping down, so it is in the filter. Looking at the filter nothing can naturally be seen. I made further tests, turning the filter 180 degrees places the smudge to the right side. Shooting without it picture is tack sharp, of course. Bigger filter on Nikon looks OK.

Has anybody else come across a similar thing or is this just a singular incident? I am returning the filter for replacement, of course.

Here is a 2x crop from the lower left corner. 30 sec at f:16, 200 ISO.