The new engine version with the new exposure settings and sky atmosphere has made this - yet again - an issue.
Granted, I imported the character, so I may be missing some basic settings.
The issue is actually the sub surface scattering. Illustraded here.
In this shot, the sun is directly behind the head. Thus, the hair we see as lit by the ear should be completely dark.
Naturally, this could also now be due to the fact that the changes I had made to the material to avoid the shine by sampling the world normals are now no longer needed… hard to tell without a 5 hour review