Introduction
For domains that are using PHP-FPM, some changes made in cPanel's "MultiPHP Ini Editor" are not reflected. This is because when you enable PHP-FPM, php.ini changes are handled differently.
Procedure
When changing values for the system or for an individual user, you need to create specific .yaml files that store these directives. Use the documentation here to make changes for the system's PHP-FPM defaults or the domain's PHP-FPM directives.
The following articles may also be helpful when making changes to your domain's PHP-FPM values:
WHM's MultiPHP INI Editor changes are not reflecting with PHP-FPM in use