Are you able to delete your menus and then create and save a new menu? Or does this still not save?
If you have database access, you could try deleting the Cordero Pro theme mods entry, so forcing a reset.
DELETE FROM wp_options WHERE option_name = 'theme_mods_cordero-pro'
If any of these fail, please let me know which starter site content you imported. If more than one, please let me know in which order they were imported.
Thanks.