What does nginx -s reopen do

This SO Q&A sounds like it might be your issue, titled: nginx showing blank PHP pages.

Your location stanza should look similar to this:

location ~ \.php$ {
    include /path/to/fastcgi_params;
    fastcgi_pass  127.0.0.1:9000;
    fastcgi_index index.php;
    fastcgi_param SCRIPT_FILENAME /path/to/www/dir$fastcgi_script_name;
}

You have to pay special attention to the path to the script you're referencing for fastcgi_param.

References

• NGINX WITH PHP-FPM GENERATING BLANK PAGE
• Index» Networking, Server, and Protection» PHP-FPM 5.3.3 + Nginx blank page

You seem to confuse enable, start and mask operations.

• systemctl start, systemctl stop: starts (stops) the unit in question immediately;
• systemctl enable, systemctl disable: marks (unmarks) the unit for autostart at boot time (in a unit-specific manner, described in its [Install] section);
• systemctl mask, systemctl unmask: disallows (allows) all and any attempts to start the unit in question (either manually or as a dependency of any other unit, including the dependencies of the default boot target). Note that marking for autostart in systemd is implemented by adding an artificial dependency from the default boot target to the unit in question, so "mask" also disallows autostarting.

So, these all are distinct operations. Of these, you want systemctl enable.

Ref.: systemctl(1).

More: Lennart Poettering (2011-03-02). "The Three Levels of Off". systemd for Administrators. 0pointer.de.