ND Filter - Pink Line?

[Sarah Allyn Photo]

I just recently purchased a Formatt Hitech 95mm Firecrest solid ND filter (2.7/9-stop) for my D810 and have been coming up with a pink line in my photos (happens regardless of shooting into the sun/light or not).
Any ideas as to what my problem is? I'm using it with my 15mm Irix full frame f/2.4.

Here's an example (I bumped exposure up so it is more easily visible);

ND Pink Line by Sarah Allyn, on Flickr

 

[480sparky25]

Light coming in through the viewfinder. Cover it up and problem solved.

 

[Sarah Allyn Photo]

Light coming in through the viewfinder. Cover it up and problem solved.

I will make sure to do that, thank you!!

 

[tirediron]

Use the viewfinder shutter; (little lever next to the eyepiece).