this is happening because you are redirecting http to https
in the mediarss.php file change:
$WAGLOBAL_Root_URL = ((isset($_SERVER['SERVER_PROTOCOL']) && strpos($_SERVER['SERVER_PROTOCOL'], 'HTTPS') !== false) ? 'https://' : 'http://') . $_SERVER['SERVER_NAME'] .( (isset($_SERVER['SERVER_PORT'])&& $_SERVER['SERVER_PORT'] != 80)?":".$_SERVER['SERVER_PORT']:"") . $assumedRoot;
to:
$WAGLOBAL_Root_URL = 'https://' . $_SERVER['SERVER_NAME'] . $assumedRoot;
you will also need to make this change in the galleries/global.php file.