I have not noticed this before. See screenshots. After Debayering I went to Blink to inspect the images. Used the Intensity Transformation "Screen Transfer Function" to fix the green color. While it did work, notice the stark difference in the background. The first image has a noisier background, which is what I am used to at this point, but the 2-31st images have a very black background. I don't know what happened. I am following the Elf's video again for this. I erased my Calibrated Lights and Cosmetic Corrected Lights and re-did them (neither had the background difference when inspected in Blink). When I finished Debayering the same thing happened.
I have no idea what is happening here.
Subs were taken at 180sec exposures, gain 120, temp -20c (this is what I already have darks for; I'll be doing new darks for either 0c temp, or -10c temp, and probably some shorter exposures just to experiment with).