Half of structure lit unevenly

So here’s the deal. I have this structure in my scene. As I moved along one of its walls I noticed that, although it is evenly lit, the lighting becomes darker from east to west (or right to left in the pics). Also, the structure has an underground floor - which is a separate fbx - that has no windows and therefore no Directional Light influencing it, and there the problem appears again. In the pics you see the ground floor problematic area and the underground problematic area directly below it. There is open, endless, Unreal space beyond the wall.

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Do you use any ambient cubemap or skylight?

This may be caused by it’s cube texture.

Nope. Just regular skylight :
Any other thoughts?

Sky capturing sky into cubemap, and applies it as ambient cubemap lightning.

So maybe this captured cubemap has some darker/lighter areas and applies it to your environment.

You can try to add some simple one-color material to sky s[here, build and check results.

The skysphere is an even-tone blue with some clouds. The part of it that faces the problematic area is pretty homogenous so I’m not sure that’s what’s causing the issue