This is most likely due to custom colors or custom CSS added to your site. For instance black font on a black header will appear to be an empty black banner.
To test, you can navigate to the Themes and Images settings by entering the page address directly into your browser bar:
For custom colors: add /admin/app_colors#customize_theme after the event name in your site’s URL eg:
For custom CSS: add /admin/app_colors#custom_css
Remove the custom additions and save, then confirm that your navigation tools display as expected.