I have this lighting artifact in render mode (only eevee though) that leaves a "square". Both meshes are manifold, everything is quads (no ngons, tris). The light source is an area light, but the same artifact shows from point light. Subsurface modifiers are the only modifiers that are present and even when applied the problem is still there. Here are screen shots:
Any ideas, is this only eevee stuff that I can ignore?