No problem, just I saw a similar problem with my own flats recently and went down a rabbit hole trying to work out why something I had nailed a year ago was suddenly giving me grief.
I use my 2600MC exclusively on 0 gain, and the MM on 0 gain for LRGB and 100 gain only for narrowband, I did shoot NB flats at 100 gain but a rough and ready set of sky flats this afternoon at 0 gain did better than a properly done set at 100 gain! I think it comes down to the loss of resolution where 1e=4ADC or so, the quantisation error was just too much for it to work.
What a great resource this is. Thanks Martin and Paul.
Ive been having the same issue with my QHY410c OSC camera where the flat frames are causing bizzare colour casts in a vignetting sort of pattern.
Looking at the thread has given me clues and I can see a few actions I can take.
Another question though - I'm getting error reports in DSS and ImagesPlus
where, even though I have shot frames at 6070x4046 pixels, these programs report differing frame sizes (6070x4044) and IP cant proceed. I can acquire the frames at the same size so its not a real problem. DSS does proceed however, so it is a work around. Just makes me wonder why???
Thought I'd post a couple of pics that show the results with the poor flats.
Horsehead nebula , 11x270s QHY410c, low gain mode, gain53,9degrees, ED100, SharpCap, dithered. Stacked in DSS.
One processed in SIRIL and noise reduced in ImagesPlus.
Second processed in Startools.
Cropped out a lot of vignetting rubbish...
I tried reducing gain to zero and differing exposure lengths. Gain didnt seem to change the flats but there was some improvement lowering the exposure time towards ADU range 8-12k so I'll work with that.