Activating the CDN will adjust the website's DNS settings. Because of the way the DNS works, it can take up to 24 hours for the customisations to be active everywhere and to be recognised by Website-Checker.
If Website-Checker still does not recognise the CDN after 24 hours, make sure the CDN is activated for the correct domain.
Please note: CDN is active for subdomains (e.g. www.your-domain.co.uk). In order for your site to benefit from CDN, it must be accessible under a subdomain – ideally under www.your-domain.co.uk. If your website has a redirect from www.your-domain.co.uk to your-domain.co.uk, you need to disable this redirect to take advantage of CDN.