I work with Substance Painter 2019.3.3. When I bake normal maps for modular assets I often run into this problem, where the normal map gradually darkens one side of the mesh like as if a light source is placed in the opposite direction. This becomes very strange when multiple modular assets are placed side by side. I have tried my luck resetting and unifying face normals on the mesh but that does not help. Any help to resolve this issue is much appreciated. I have attached a screenshot describing the issue.