As a test, I deleted the top floor, which was built with BP_Floor_Builder blueprint, and built one piece by piece using the identical assets in the pack. I then rebuilt the lighting. As you can see, the dark spots only appear on the bottom floor (BP_Floor_Builder) and the top floor built by me renders correctly without spots. I assume that this is a bug in the BP_Floor_Builder blueprint tool and I have reported it to the pack designer.
