Você precisa adicionar um bloqueio ao seu bloco com um fastcgi_index
set:
location ~ ^/_status$ {
include fastcgi_params
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_index index.php;
fastcgi_pass unix:/var/run/php/php7.0-fpm.sock;
# the following is optional but nice to have
# it will restrict access to the local monitoring system
access_log off;
allow 127.0.0.1;
allow ::1;
deny all;
}