Im getting strange lightmass builds on datasmith imports. Some objects have issues but unreal shows no errors in the log.
Sometimes objects appear really bright or black.
Well your floor’s lightmap resolution is low…
Are you talking about the left lower side of the furniture? Or the dark in the middle? :S
Black result usually missing lightmap/wrong channel
Too bright: flipped normals.
Its not flipped normals. I mean the variation on the cupboard surround and inner face. When I rotate the mesh and re-bake the following happens. i’m stumped.
I’ve also noticed that if I turn off the skylight those face render black, the nornals still seem fine though.
Ooookkkey
So what lights do you have in your scene? All of them are static/statioanry?
Can you show me/us the lightmap for this object?
Can you show me/us your lightmass settings?
Are you using Lightmass Importance Volume?
All lights are static, The above test is just done with just sunlight.
Lightmass setting are default for this test with medium build quality.
yes using a lightmass volume.
uvs below.
Ive tried importing the same mesh with custom uvs and fbx. same issue. 
Is the mesh closed? I mean it’s not just made of planes but closed 3d rectangles…
Have you tried to visualize the samples? …it looks like if there are no samples at those areas…
What is your lightmap resolution?
How do I visualise samples on the mesh? Mesh is closed. Light map res is about 1k, light orange to visualise. I notice this happens with the same mesh as fbx import, it could have errored uvs still look fine.
I’ve found that rotating the mesh in max and reseting the xfom fixes the issue but only on one axis. It maybe some sort of node transform issue.