In editor: when you import in the editor it might take time for textures to show as UE is compiling shaders and that step can be slow.
That is also true if you import while playing in editor, it takes time to process texture.
In a packaged application, the material building is limited and it happens that materials do not all look as they are in editor. Usually people will replace material loaded on the fly by materials that has been packaged along the application.
Do you see any warning or errors in your log file when you import in a packaged application?