Some few users have duplicated menu items after Demo Contents import. This happen cause the server goes in time out in the import process. Without stop the import Uncode re-start the upload silently in the background again so it can complete. Every time the upload start the menu is automatically imported and cannot be stopped. For pages and media Uncode can check if the item is imported and it does not import again.
To fix this please go in the WordPress menu editor, delete the main menu (just 1 click), than import the Demo Contents again. Uncode will import only what it does not find for the contents: the main menu. You end with a nice menu in seconds.