I've found that the server returns incorrect MIME content type for rss feed (Content-Type:text/html; charset=utf-8) - it should be either "application/rss+xml" or "application/atom+xml".
Some rss clients (including the one built-in in Sonarr) are ignoring the feed if the content type in header is incorrect.
I'm not sure whether it is problem with Apache server configuration or the content and headers are generated by some script (probably PHP) but the fix should be relatively easy to implement.
Thanks.
