ND Filter colour cast

I recently got some new Formatt Hitech ND filters

This is the first time I've used these.

This was taken with a 6 second exposure with a 3.0 ND filter

You can see the strong colour cast which I have not experienced with my other ND filters.

Changing WB settings did not make it go away

Trying to fix in Post has not been highly successfull.

Does anyone know what is happening here?

Does anyone have an idea what to adjust in LR or PS to fix it.

TIA

--
nicholas