First of all many thanks to you all for the work you’re putting in for hopefully finally achieving a solution…
@MostHost_LA: Originally I thought recomputing tangents wouldn’t work.
After having done some tests, it works technically, but only in “inclusive” mode of default skin cache behavior and with support compute skincache checked as well of course. Unfortunately the resulting seams are really terrible.
The most promising of those solutions you have presented seems to be the one with increasing the indirect lighting intensity, but unfortunately it works only with stationary lights and I need movable lights, because my world has a dynamic day-night cycle with a moving sun.
@FrankieV: I looked into DAZ and there really are some artifacts on the g8 mesh in the armpit area (like in your video), esp. if the body has no subdivisions applied, but strangely the mesh looks clean in blender and ue, if you just look at the topology (wireframe mode).
The skin in unlit mode looks clean as well, so the strange artifact isn’t necessarily causing the shadow problems since those artifacts would be visible on the topology (wireframe mode, unlit mode…) as well.
Strangely enough Genesis 3 neither has those artifacts (in DAZ) nor has it those ugly shadows in UE4, although g3 and g8 share the same topology (except for the nails,eyes?).
But the reason could be a different one than you may think, because G3 characters come with the t-pose and G8 chars come with the a-pose, so the necessary bone rotation and thus extent of the corresponding corrective shape key (JCM) is a smaller one for G3 chars than it is for G8 chars for the arms up pose.
Consequently you will encounter more shadow problems where the extent of shape key intervention is bigger and it certainly is bigger with G8 chars as the distance from the arms up pose to the a-pose is a larger one than it is in relation to the t-pose. MostHost_LA’s posts suggest that the issue could equally lie with UE4.
Btw I’m using UE 4.25.1 Dual Quaternion Mod, are you using the same version?