Hi Brain, Ortho,
Thanks for using Super RSS Reader.
This issue might happen when the SSL certificate of the RSS feed URL had expired or something similar. A quick Google search confirms the same.
Since the plugin didn’t receive any update in last 2-3 weeks there shouldn’t be any issue with the plugin, but with your website’s SSL certificate (or) the RSS feed URL’s SSL certificate.
You can contact the RSS feed owner and inform them the same.
As a workaround, can you please use a http:// URL instead of https:// URL for the RSS feed ?
Thanks,
Aakash