Hello everybody! I am a new user of UE4, but have been familiar with 3ds Max and V-Ray for quite some time now, so as many I have decided to switch to real-time architectural visualization with UE4.
I followed a lot of tutorials on how UE4 works and the workflow with Datasmith.
However, I try to train on already existing V-Ray scenes, and I will show you as an example here Scene 2 of Volume 37 from Archinterior by Evermotion.

So I export the whole scene with Datasmith which I import into UE4.
o far no worries. I'm preparing my scene a bit: Reflection Sphere Capture, Skylight, Post Process, Volume, Lightmass Portal and Lightmass Importance Volume.
I also try to optimize the Light map Resolution by object quite quickly (below).

And when I build (no matter the quality) I always end up with this kind of result:

in my opinion this is a UV problem. To overcome this problem, I decided to put all my objects on Channel 2 on 3ds Max. And honestly I don't have the impression that it works ... When I re-import my objects in UE4, new UVs exist, but never in Channel 2. They are found all the time in Channel 1, here is an example with the walls:

On the other hand, it would seem that when I export to FBX without going through Datasmith, UV rays are good on Channel 2. But the problem is still present..
The black books on the shelf are a backfaces problems.

I am very motivated to continue learning, but it's been 3 days that I fail in this way and it demoralizes me a little ... Help me please ​​​​​