There's a lack of shadows at the very base of the white columns, which looks very much like the occlusion rays (used when doing NEE to determine whether the sur

There's a lack of shadows at the very base of the white columns, which looks very much like the occlusion rays (used when doing NEE to determine whether the surface point is occluded or not for the light being sampled) have too large a ray epsilon or offset being applied... i.e. the very base of the white columns is pure white, as a disconnect from the rest of the columns.