Last Updated on 4 November 2022 by Daniel
This commonly is because mod_proxy_fcgi is enabled, and you are using PHP-FPM. The default error page in the proxy is one line:
File not found.
To correct, add the line below to your httpd.conf or apache2.conf file Do NOT add to your .htaccess file.
It forces your .htaccess file’s
ErrorDocument directive to override the default Proxy error page. Restart the web server afterwards.
If you use WHM / cPanel, then see the article here: