If you use ArvaCloud's CDN product and due to its reverse proxy, your origin server will receive the traffic from ArvanCloud CDN's IP addresses instead of your IP address. This can lead the firewall of your origin or shared hosting server to detect this traffic as an attack and block ArvanCloud's CDN IPs.
In this case, the origin server will not respond to ArvanCloud's edge servers' requests, preventing visitor traffics from reaching your website.
To avoid this problem from happening, or solve it in case it has occurred, you need to whitelist all ArvanCloud IP addresses at your firewall or origin web server. Contact your hosting provider if you do not have permission to apply these changes.