It’s the contrast equalizer. I turned off almost all modules (first the ones that used masking, then tone equalizer, which itself it a tool to adjust exposure using an internally created mask), and it was still there. contrast equalizer off on the left, on on the right:
Hello Lighover
Please turn off the very first “color balance RGB”.
You will see the halo disappear
Notice: I mean Color balance RGB 0 and not Color balance RGB 1