TOPIC:

I got to the bottom of this issue. It was certificate related on the server. The issue was due to a broken certificate chain. It appears that the certificate for the site was valid and browsers were happy with that. The RSS page uses the Snoopy class and the 'stream_socket_client' method which requires an secure connection and checks the entire certificate chain and will fail if there are any issues.

You can run the following command in the terminal "openssl s_client -connect fully.qualified.domain.name:port" which will indicate if there are issues in your certificate chain.

Hope this helps other users going forward.