The white walls in this scene share the same world aligned material. The outside walls (red circle) are stationary and show a strange vignetting on the bottom whereas the smaller wall part between them is set to static and baked lighting looks as it should.
We disabled all post effects and AO. We use a stationary directional light and a static sky light.
Does anybody have an idea what could cause this?
Lighting problems such as this one can come from a lot of different variables. Your best bet is to use the visualization tools Unreal offers to determine where it is coming from. In your viewport, you can go under “Show” → “Lighting Components” or “Light Features” to toggle through and see which one may be causing the issue. You may also be able to find it under the various visualization view modes (the one that is “Lit” by default.)
That said, Stationary Objects and Static Objects are going to handle lighting differently and getting a perfect match may not be too easy. For the most consistent look, you will probably want to make sure the entire wall is set to be the same.