Generating UVs in UE4 only works if you are using a single texture or material applied to the mesh. If you have meticulously unwrapped and painted your texture to match the UV’s you created in your 3D app, it’s going to be all undone with UE4’s UV generation. The best practice is to unwrap properly in your 3D app with enough space surrounding the UV’s and to create a 2nd set for the UV lightmap channel.