GPU Ligtmass Lighting Bake Issue

Hi folks, I have decided to use GPU Lightmass for my latest interior architectural viz project and this is what I am getting. I like how fast it is to work with, however I have never seen such a problem before. This wall is just a cube of Unreal Engine’s. The wall I have removed had the same issue, thus I thought it was about the UVs but seems like not. its lightmap resolution is 2048 and set to right UVs from its props.

I need your help people!

Thank you.