No, the website is offline. I think all config is all right (I have managed to show a placemark list very easily, so group list should not be a problem). There is no error message in the console when the page is loaded.
What is important is that a map is placed in the article via plugin. Maybe this has something to do with the issue? I have done a lookup on your php code for the plugin and the component and I have found out that for the component, when map has proper attribute, you import placemarkgroup.css file, but I could not find that kind of code in the plugin php files (css for placemark list is imported in both component and plugin code).
OK, so this is solved, sorry I did not find it in the docs, I have started to use our plugin (and Joomla CMS) just yesterday, so I am "green" with some topics.
Am a programmer and yes, plugin and component have duplicate code Maybe I will refactor your code by myself... Just kidding! A am thinking about adding some new features, like custom order of placemarks on the list, or autocenter and zoom in to the pacemark after click on the list.
One last thing - do you know how can I place a map in the article without the plugin?
By the way - your product is realy good, I will donate whenever possible.