I had the same problem, except it was on the floor mesh of the third person shooter, template map. I modified it in the mesh editor, but didn’t apply textures. Then it was black in the editor viewport (4.24.3) and I hadn’t changed much else. I finally tried enabling “Dynamic Inset Shadow” and that brought it to lit. I was trying to set up the Light Propagation Volume in an RT-enabled scene, with MDF enabled too.
Now I have a problem where when moving the camera around the mesh, it changes color as though it has a desaturation filter getting rendered over it within a certain view location of the camera.