One reason:
Check configuration "user" and "group" in php-fpm.conf
Default they are set by "nobody".
If you start PHP-FPM with another user before (such as: phpUser), then you stop and start again with root privileges.
--> Child process will be run with user "nobody" --> They cannot access some folder that "phpUser" created before.
Fix: Make sure you run PHP-FPM with a single user.
