[php] Turn off display errors using file "php.ini"

It is not enough in case of PHP fpm. It was one more configuration file which can enable display_error. You should find www.conf. In my case it is in directory /etc/php/7.1/fpm/pool.d/

You should find php_flag[display_errors] = on and disable it, php_flag[display_errors] = off. This should solve the issue.