I'm hoping there will be a few others who have experienced this issue and may shed some light on the problem:
I edit my portraits in LR2015. When I then export to PS2020 for further editing a colour shift takes place. The skin becomes more saturated (not ideal) and there is a subtle contrast boost overall. This appears to be a recent issue.
Lightroom is currently instructed to use the following details when editing externally in PS: