I downloaded some world space based landscape materials which work fine on any of the in game geometry meshes. When I apply this to some imported objects the material only shows up as the grey checkerboard material. The objects were created in sketchup but had uvs assigned correctly with a uv tool, which may or may not be necessary as these materials are meant to work on world space co-ords.
The standard ue4 materials assign to these objects just fine so its something to do with there being some kind of world space relationship context missing. I notice if I look for a size map for these sketchup objects its listed as missing. Whether that is relevant or not Im not sure.