Why i have black 1 wall?

Hello,
i have problem with wall in simple test file (im learning UE). All walls looks good but one side is always black. Can explain me why???
Walls model i made in 3dsmax. For UVWrap i used “SteamRoller” on 2 channel. To Export model i used UE4 FBX export. Model has one white material.
Please help me.
Me english not very good so if you can explain me in very simple words or pictures I will be grateful.
Thank you!

As I can see, you have not built your lighting. You have a red warning in the left corner of your viewport “lighting needs to be rebuilt” and all your shadows has “preview” status. Firts of all, add skylight with mobility “stationary” into your level, this will make the shadows not so dark. If you already have one and your shadows are still dark, choose mobility “Moveble” and then reset Mobility setting to default (yellow arrow on the right). Notice, Skylight requires atmospheric fog or SkySphere. Then build your lighting, go to tab “build”, set production lighting quality and press “build lighting only”. If you want better shadows quality, you can adjust Light Map Resolution in Static Mesh Settings (must be power of 2 (64,128,256)).

203653-skylight.png

https://docs.unrealengine.com/latest/images/Engine/QuickStart/6/productionLighting.jpg