Hi Paul,
I went to your latest FIT files here.
https://drive.google.com/drive/folde...a_DeQ3gURtM4la
I've examined the darks and the flats.
I can see no evidence of diagonal lines in the darks or flats.
I am wondering if the diagonal lines are caused by either:
(1) a gradient in the sky or
(2) some kind of magnetic field in the camera?
Those lines are way down in the noise & I easily processed them out.
I attach a highly stretched version of the master flat for Luminance.
It's processed to show dust doughnuts and I can see a checkered pattern noise.