There is no requirement to log into cPanel per se. You have to sign in to the single sign-on page. That is the only thing that counts as "activity" at the moment. Once you've seen "Sign in Successful", you're golden. That still doesn't let you maintain your site, so there's still a problem between you and the server. Either port 2083 is blocked in a firewall somewhere or your AV software is throwing a tantrum - there's nothing wrong with the certificate, unless a lack of public audit records is a "problem". The CA chain is intact, current and verified. If that's not enough for Avast, it's being overly aggressive.