Can't get Advanced Theme Switcher to work

I have created a demo site to use with the Advanced Theme Switcher. There are 21 themes available under the Themes menu (they are all child themes - the parent themes are not network enabled). I activated the Advanced Theme Switcher for that site and added the plugin to the home page. But when I go to the site, there is just the heading "Theme Switcher" but there is no dropdown (or list - tried it both ways) below it. There is nothing in the html code of the page other than the heading. Please advise.