Ok, from your random explanation i see that you up-convert Rec709 source to Log and adjust Gain in Log gamma:
Rec709/Rec.709-A to RWG/Log3G10 -> Gain -> RWG/Log3G10 to Rec709/Rec709 Luma and Saturation Mapping turned ON
What did you expect of this? If you don't like Log3G10 Log curve response, change Log3G10 to ACEScct in both CST nodes. Different Log curves provide slightly different response for tools:
Rec709/Rec.709-A to RWG/ACEScct -> Gain -> RWG/ACEScct to Rec709/Rec709 Luma and Saturation Mapping turned ON