If you are having trouble with SSL warnings while connecting to your WHM, cPanel, or webmail services the quickest and easiest solution is to not force an SSL login – the SSL login would certainly still be available, but is not required.

You can change this in WHM >> Tweak Settings >> Security section.

The second best solution would be to install an SSL certificate to WHM [NOT through a cPanel account domain] for the server’s hostname. Make sure that the DNS for hostname.com resolves correctly, then go to WHM >> Tweak Settings >> Redirection and change as follows:
“Always redirect to SSL: On”
“Non-SSL Redirect Destination: Hostname.”