Lightmap problem after building

Greetings!

I am currently creating a virtual walkthrough for archviz.
My project it build in 3DS MAX and exported to UE using Datasmith.
My scene has a directional light, a sky light, and some point lights.
After building my light, i noticed that one of my walls is a different colour (gray rather than white)

Here are some screenshots to illustrate my problem:

  1. Full light setup

2.Directional and sky lights ON

3.Point light ON

4.Unlit viewport

5.Lightmap density

Here is some more information.
All my light are set to stationary.
When I set my Directional and sky lights to movable, the problem seems to disappear, but my lightning has poor quality.
Additionally I have a BP_Sky_Sphere from the FPS level, a lightmassimportence volume and a post process volume, with default settings.

I am relatively new to unreal and the problem may be with a really simple solution, but couldn’t figure it out on my own. Any help will be appreciated. Thanks in advance.

Greeting again.

It has been almost 2 weeks, but my problem still persists.
Even more so, I have a colleague at work that has the same problem with a completely different scene.

After some consideration we arrived at the conclusion that it has something to do with the version (either of Datasmith or UE), because one scene that worked fine in 4.18, had the problem after importing it to 4.19.
I tried the new 4.20 preview, but the problem was not fixed (I created a new project and imported the old datasmith file).
I will try re-exporting it from 3DS max and importing it to ue again, but I doubt there will be any difference.

If anyone can help and give me some leads as to where to look, I would be very grateful.