Operating system: Windows 10
Graphics card: GTX 1080 ti
Broken: 2.90.0 b21ba5e5795 (Jun. 28th, 2020 Windows buildbot) and all others tested back to 2.79.6 66ad9ef2ce3 (Sep. 14th 2018 Windows buildbot)
Working: none known
Short description of error
On a Cycles material with random walk subsurface scattering, and subsurface radius that is small relative to the geometry's distance to the origin, and the faces that have normal components significantly parallel or antiparallel to the direction to the origin see significant darkening relative to the shader's isotropic behavior near the origin.
Exact steps for others to reproduce the error
Put a UV sphere at location (1000,0,0) and put a Cycles material on it: principled BSDF with subsurface component 1.0 and subsurface radius scaled down by 100 from default to (0.01,0.002,0.001) and observe that all the faces except a longitudinal ring in a plane normal to the vector to the origin become much darker brown than they would be if the sphere were at the origin.
(Shown in attached .blend file)