Aha, you have more than 25 lists??? I just checked and the list call that we make to mailchimp has a limit set to 25. Are you sure that when you duplicate a list it shows in CMC? Is it possible that it shows, because this list now gets on top of the queue, but some other list is missing?
Try the following: administrator\components\com_cmc\controllers\sync.json.php on line 46 you have this:$listStats = $chimp->lists(array('list_id' => $lists));
change it to:$listStats = $chimp->lists(array('list_id' => $lists),0 , 100);
Do you see your list now?
Regards,
Daniel