The URL for update checks was https://s-plugins.com:8080/
However, we have replaced it with the one without port number. I didn’t know outgoing connections to some ports could be blocked. I can understand if a server is blocking INCOMING connections, but why outgoing?…
Anyway, a new stable version (2.0.15) will be released soon (within 24 hours from now) and it should have this issue resolved. Thank you for reporting and helping to investigate this.
Also now you know that Siteground blocks all ports but those it has white-listed.