MailChimp Pro - Toubleshooting groups not appearing in list
If you create a brand new group in MailChimp it may not immediately appear in the RCP MailChimp Pro settings. This is because the group list results are cached for one day to avoid querying MailChimp on every page load.
You can forcibly delete the cache now by installing the plugin Transients Manager. Once installed, go to Tools > Transients and search for a transient starting with "rcp_mailchimp_pro_list_groups_". In the results the list ID will be appended to the transient name. You can delete any results starting with "rcp_mailchimp_pro_list_groups_". This will force the plugin to fetch new values.