An imported asset has Lightmap UV are overlapping by 80.8%. Please adjust content -Enable error coloring to visualize. I am unsure how to enable this error coloring or fix the Lightmap UV.
You can enable it in the “build” dropdown menu - use error colouring 
You have to create a proper lightmap in your 3d progam: ://
Oh well that is annoying. It was in one of the items I was using from a marketplace asset. What exactly does error coloring do?