Recently there was an issue where the fopen and curl function and shell_exec functions were reverting back to original values. Using the MutiPHP Editor was not working.

the resolution was that the php-fmp handler was being used on a cpanel server. So the php-fpm config file needed to be changed.

The line that needs to be edited is:in /opt/cpanel/ea-php56/root/etc/php-fpm.d/$DOMAIN

Remove the disable_functions which includes shell_exec

php_admin_value[disable_functions] =

Then restart the following services.

systemctl restart httpd.service
/scripts/restartsrv_apache_php_fpm
/scripts/restartsrv_cpanel_php_fpm

UPDATE; Seems the yaml files need to be updated:
https://forums.cpanel.net/threads/stop-cpanel-from-overwriting-php-fpm-settings-file.596527/

This information is for editing the yaml file which should result in permanent changes.

More information here on php-fpm configurations:
https://documentation.cpanel.net/display/64Docs/Configurations+Values+of+PHP-FPM#ConfigurationsValuesofPHP-FPM-Howtoremovedefaultvaluesfromaconfiguration

UPDATE 2:

Also, there was an issue with fopen where the changes in the MultiPHP Editor were being overwritten.

If  PHP handler is LSAPI, you can adjustment to your Apache configuration. Please ensure the setting is enabled for the site(s) in question under MultiPHP Ini Editor. If this still does not work, in whm from   Home »Software »MultiPHP Manager there is a System PHP-FPM Configuration tab and from it you can change the user override ability for allow_url_fopen and other options.