Terrain problem


I recently started learning UE and everything seemed pretty simple. I have the skills to work in 3D Max (20 years), as well as in Unity, 3D Coat and various other programs. Because from UE I did not see any tricks and studied a lot of video lessons and started working with the engine.
I had to make a terrain based on a heightmap that I had prepared in advance in Bryce and Photoshop. I just wanted to make some adjustments and render the landscape along with the sky.

The landscape turned out, only black, although I tried to impose different materials on it, but it does not matter. When I opened the project the next day, I saw this.

In addition, the camera I set up for the render is missing.

What I did wrong? And just in case, can I export the landscape to a mesh with material?

Thanks for your attention.