Lightmaps were generated with the On Demand GI Workflow from a scene lit only by a Skybox (or only by Sky Light Color). The scene is a collection of cubes. One of these is uniformly scaled, and one of its faces is in the same plane as adjacent faces on non-uniformly scaled cubes. The faces of the non-uniformly scaled cubes are black, but the face of the uniformly scaled cube is much lighter. The same material is applied to all of the cubes in this scene.