I also tried logging to syslog:
error_log = syslog
In pool.d/www.conf comment out:
It didn't display anything in the syslog after testing executing invalid code.
Apparently if error_log is commented out, it should default to sending logs to the nginx error log. That didn't work either.
Logging is definitely enabled and the log locations have been confirmed with:
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> * www.conf
> * php-fpm.conf
> * php.ini