I´m going crazy with this problem - perhaps you can help. I´ve got a very simple scene, just a mesh for walls (5x5 meters), one for the ceiling and one for the floor. All meshes are about 20 cm thick and the whole room is closed, without any leaks.
I added a directional light, fog and skylight. The baked scene inside the room is completely black without any light leaking - and this is correct. But my moveable character picks up some light from somewhere . I also decreased the number of the detail cell size - this helped a bit, but still some lighting on the character appears.
Not expert, but I think this is limitation of Volumetric light map. No matter how much you decrease the cell size, 20 cm wall is too thin. I tested it in 4.19 and best thickness was more than 50 cm.
You can try add a light blocker. I know you have no leaks in the scene but it might help in this scenario. Also try changing the detail cell size in Lightmass settings to something like 50 (not sure how far you went with the value), worked for my scene with almost similar issue
Start disabling elements in the viewport options to see if it’s from Volumetric Lightmaps/Indirect Lighting Cache or from an actual light leaking. Depending on your shadow settings in your directional light, your dynamic objects may not be shadowed even though the static environment is.
Have you tried see if the reflections are correct on the inside? Try put in a Sphere Reflection Volume and see if it helps. Eventually check the reflections buffer vizualisation
Old post but let me drop my solution for laters.
You can see you character shining like a light bulb even in the deepest, darkest cave.
That must be because of skylight. Try to turn it off.
For interior and exterior scenes together in a map, you can use a postprocess volume for all your interiors to tweak the light.
I remember making trigger volume blueprints for interiors which finds the lighting components in the map(weak references) and tweaks them for interiors on begin overlap.
Unfortunately there is no one4all solution for this. Because interior and exterior lightings are different.
Refer to Soul: Cave, Realistic Rendering, Epic Zen Garden example contents for some clue about overall daytime lighting.
. I also decreased the number of the detail cell size - this helped a bit, but still some lighting on the character appears.