This is the basement in my project. 2 questions. If this is a dynamic lighting only map, why is my light-less basement not completely black? Why is it lit at all? And what ar
e those dark lines/artifacts on the floor in the screenshot?
It could be Auto Exposure. You can probably turn it off in the project settings, but if not, then for sure you can with a post process volume.
Like Detach say, could be auto-exposure.
Could also be skylight, it gets everywhere. The only solution I found was to use a dynamic skylight and enable mesh distance fields.
Which incidentally, your artifacts look like MDF problems. You could try changing the ‘distance field self shadow bias’ in the mesh settings.