error: The loopback request to your site failed

Yes, it’s a server configuration issue. The message means the server cannot make a HTTP request to itself through the cURL package. cURL allows PHP to make requests to its own server and other servers using various protocols like HTTPS, FTP, telnet, etc. It’s possibly a problem with modSecurity configuration, though there are numerous other possible reasons.

Whether the failure affects you or not depends on what WP functionality you use. It’s usually related to backend functionality and rarely affects frontend functionality AFAIK.

In asking your host for help, I’d just give them a copy of the site health message itself. They should know about cURL and loopbacks. No further explanation is necessary.

Checked all plugins one by one and Found two plugins cause the same 3 critical errors report in site health.
1) An active PHP session was detected
2) The REST API encountered an error
3) Your site could not complete a loopback request

Hope developers can fix it soon.

@cfm168 – Thanks for the update.

Which 3 plugins cause those errors? It would be helpful to know.

Thanks!

@roam92
I found one plugin named Woocommerce Product Designer has php sessions issue. Deactivate it all issues are resolved. Developer promised to fix this problem but still persists without any further response almost two months now.

Replace session_start() with the following in the plugin config file…

//@session_start();

session_start([
‘read_and_close’ => true,
]);