Material loses texture in Content browser


May be you can help me here.

I have imported the Nature package from this thread:

The problems is that when I select a material or a mesh in the content browser, it loses its texture/color and becomes grey/black. (It works fine with the meshes of the starter content)

It’s the same if I drag & drop the mesh in the Foliage window, the texture is also lost.

Do you have any idea where it could come from?

Unreal Engine version 4.18.3