There from above (see the second widget, please), there is information such:
Your theme has 2 other widget areas, but this particular page doesn’t display them.
You can navigate to other pages on your site while using the Customizer to view and edit the widgets displayed on those pages.
But after all in Appearance => Customize => Widgets there is no reason for the mandatory functions of the main page Home Main Content Are, as well as Single After Vontent. Without them, I can not edit the main page. Please see the screenshot