Has anyone found a way to fix the problem? Increasing the subdivisions the artifacts remains, less visible because the polygons are smaller. I have also attached Arnold image (Redshift is very similar) even with less subdivisions and more contrast that work better.
From blender 2.90, you can tweak this using the Object's Shadow Terminator Offset Shading property.
Terminator artifacts are a complicated topic of raytracing. From a technical point of view the normal of the face shows the way from the light source. Therefore the face is not illuminated by light and a shadow is cast at the right place. Even if it is technically expected behavior and does not mean a "bug" - from the user's point of view this is often not the desired effect of smooth shading.
Simple measures to work around the problem are:
- More geometry through subdevision
- or create the normals with a high resolution mesh and back to the low res mesh
- large area lighting