A few days after creating a cert for my domain I received an email from Google:
Google has detected that the current SSL/TLS certificate used on https://www.example.com/ does not include https://www.example.com/ domain name. This means that your website is not perceived as secure by some browsers.
Without your domain name it’s tricky to be able to help fully.
Is the certificate for the domain with and without the www ? do you have a www version of your domain name ? Do you have a redirect / preference for if people use the www or not ?