Hello,

as it's always said, ranking has nothing to do with indexing and sitemaps.
If your site ranked higher in the past, it means that you have experimented a rank decrease probably due to the recent changes in Google Penguin. Also take care that from January the SSL become a rank factor for Google.

However, submitting and resubmitting a sitemap can't lead to penalties, however normally it's not needed because Google and other search engines fetches the sitemap automatically every 1-2 days. You may want to resubmit it to speed up indexing of new links in particualr cases, for example if you have a lot of changes and new contents added.

Best regards

John D.