What you have is more related to content creation issues that have been pointed out here in this thread.
4.12 on the left, 4.13 on the right
This is the template floor from the default level using a basic white material and a 256 lightmap resolution and there is a little bit of bleed due the floor having part of it’s faces outside in the light. I only used higher lightmap resolution to limit light bleed with this copied floor mesh.
This scene is lit entirely by the skylight with no directional light. This looks correct to me.
These are the settings used in the skylight.
You wil want to troubleshoot your level and make sure that you are developing your content correctly. Using some or all of the suggestions made previously in this thread would be a good start.