Set your site domain to either www or non-www
A commonly neglected site configuration is to allow both www and non-www traffic. Per Google, this causes problems with indexing, and possibly security warnings depending on the configuration of the SSL certificate.
This ultimately should be configured in the site's
.htaccess file with a RewriteRule, but can be easily handled with a Cloudflare page rule. For example, the page rule for this site:
This rule will take any requests to the non-www URL and 301 redirect them to www.