Lightmass burns strange artifatcts or problem with baking.

Hello there,

I am doing my first archviz project in UE4. When I did lightmass calculation I got very strange issues. It seems like some kind of reflection was by mistake baked into lightmaps??
I have never seen anything like this and i am stuck with this problem.
Dear UE4 community, please help me to find a way to solve this issue!