noise floor and flatfield correction

Got this milky way stack that I am trying to process, and I am really getting stumped on workflow. I have a 100+ image star stack and panorama, with an additional 17 dark frames, definitely gathering enough light for a decent result when everything is properly processed. All shot on a 50mm at f2 on a Sony A7ii

However, on the processing side, I am running into issues. There is significant vignetting, for which I have a good flatfield for. However, when I apply the flatfield, it raises the near noise floor non-linearities such that the corners have a bright magenta reverse vignette, from some positive offset, kind of like seen in this thread, Huawei DNG files and flat field correction in rawtheapee produces a purple vignette [solved]. However, I am using a dev version of Rawtherapee released after the referenced fix in the thread, yet the problem remains. I have also played with clip control in the flatfield options, as well as black points, but nothing seems to work.

When I do the stacking directly from the raw files instead of Rawtherapee tiff output in Siril, the problem still exists, but is somewhat reduced. I however loose on color calibration, demosaicing, chromatic aberration corrections and other raw only processing parameters that are well controlled in Rawtherapee.

Any advice?
Sample light frame:
DSC07178.ARW (24.1 MB)