Why exported landcape loses its material

Hi all! I’m trying to export my landscape as a static mesh (File → Export Selected) but whenever I do that, Unreal 4 creates an object without material (it’s just gray or black or it is a reflection of sky box; material initially attached to the exported landscape is nowhere to be found on it).

Sometimes Unreal just hangs for a few minutes and does nothing after that and once the exported “landcape” (static mesh) was positioned vertically and was rotated (oO).

What am I doing wrong?