WordPress Admin Dashboard is not displayed properly on a website hosted in Plesk: "access forbidden by rule" or "client denied by server configuration"

Plesk for Windows Plesk for Linux kb: technical ext: wptk ABT: Group A

Applicable to:

WordPress Admin Dashboard is not displayed properly: layout is broken, css/js scripts are not loaded.
One of the following error messages appear in domain's log at Domains > example.com > Logs:

CONFIG_TEXT: access forbidden by rule, client: 203.0.113.2, server: example.com, request: "GET /wp-admin/load-scripts.php?... HTTP/2.0", host: "example.com", referrer: "https://example.com/wp-admin/update-core.php"

CONFIG_TEXT: AH01630: client denied by server configuration: /var/www/vhosts/example.com/httpdocs/wp-admin/load-scripts.php, referer: https://example.com/wp-admin/

If LiteSpeed is used instead of Apache, the following error message appears in /var/www/vhosts/example.com/logs/error_log:

CONFIG_TEXT: [ACL] Access to context [/wp-admin/] is denied!
Browser DevTools (F12) > Console tab shows that load-styles.php and/or load-scripts.php cannot be processed by a web-browser with a 403 Forbidden error.

JavaScript conflict in WordPress theme or plugin.

Other options to disable scripts concatenation for WordPress admin panel:

In wp-config.php file via Plesk

Log in to Plesk.
Go to Domains > example.com > File Manager.
Open the document root and click on the wp-config.php file.
Add the following record at the end of the file before the require_once directive:

CONFIG_TEXT: define('CONCATENATE_SCRIPTS', false);
Save the changes.

In wp-config.php file via a command-line interface

Connect to the Plesk server via SSH.
Open the file /var/www/vhosts/example.com/httpdocs/wp-config.php in a text editor (for example, vi editor).
Add the following record at the end of the file before the require_once directive:

CONFIG_TEXT: define('CONCATENATE_SCRIPTS', false);
Save the changes and close the file.