Solution to random Let's Encrypt Certbot Connection refused / Invalid response Authorization Errors
Since I upgraded my Certbot from version 1.7.0 to 1.11.0, I was getting different errors with different domain names when executing certbot renew command.
When renewing webfoobar.com:
certbot renew --cert-name webfoobar.com --dry-run
I get Invalid response AuthorizationError: