Just downloaded the latest version of the App and noticed that it has an update note "Mandate Secure Communication".
This is posted as last update 28/1/2019 so the forced secure connection is expected behaviour.
As stated on Books OnLine "A valid SSL certificate signed by a trusted certificate authority is required, for example, VeriSign. If your certificate is self-signed, log on will fail." (http://documentation.commvault.com/commvault/v11/article?p=41313.htm)