Something wrong with shadows, lightmaps

Hi. I’m wondering about it for a while so I’ll ask you.
I have a building in Unity with two floors. On each floor lighing is the same (same properties and values). But in lower floor there is something wrong with shadows and/or lightmaps.
It is shown on photos.
Do you know what may be the reason of those dark pixels which I assume are shadows?

DId you build the geometry yourself with a tool like Blender? Because this looks like a problem with the mesh and it could be that there are multiple triangles in the same spot on top of each other or that a face normal points to the wrong direction.
You could also try to give the wall some depth instead it just being a plane.

Yes, I was modelling everything on my own in Maya. So you suggest to check if everything is okay with models? The other thing that I’m wondering about is the way how lights look. I mean in ‘right’ photo lights are much different when it comes to some kind of highlights on the ceiling. There is no such thing in ‘wrong’ photo. That’s why I thought it may be something wrong with lights.