As you can see on the image, there are unwanted boxes when baking the lightmaps. As shown on the scene view and the lightmap view.
I have enabled automatic generate lightmap UV on the FBX models
I have also marked everything as Static and are all contributing to global illumination.
I am using the high-Resolution Lightmap parameter.
Try using the Invalid Texels visualization mode, selectable in the top left drop down box from the scene view. The entire ground is probably marked as red, which means invalid. The most likely cause is that some large geometry (maybe the roof) is seen from behind, either meaning that the normals point in the wrong direction, or it’s single sided but the material is not set up as double sided. The blockiness stems from a flood fill algorithm that tries to cover up invalid texels by accepting results from neighboring valid texels.
