Some Content Management Systems (CMS) such as Wordpress require the PHP handler on your Plesk server to be switched to FastCGI to work smoothly. Do set this, follow the steps below for each subscription/site required.
1. First you need to Log in to your Plesk control panel.
2. Click on 'Subscriptions' -> (domain name).
3. Click on the PHP Settings
4. Change the 'PHP support (run as)' to 'FastCGI Application'.
Switch PHP Handler to PHP-FPM
As technology moves on you may have Nginx & PHP-FPm installed on your Plesk server which is a much faster webserver and PHP handler than Apache and Fastcgi. Using this may potentially make your site significantly faster as long as your web application supports it.