I am not sure what is the reason of my problem. In some cases my PHP script successfully saves data in it's own (script's) log. But there is no corresponding record in Apache access log.
Why?
The error log is empty.
mod_fcgid/2.3.9
Apache/2.4.6 (CentOS)
PHP 7.1.3
Apache config
<VirtualHost 127.0.0.1:8080>
...
CustomLog /var/www/httpd-logs/example.com.access.log combined
ErrorLog /var/www/httpd-logs/example.com.error.log
...
<FilesMatch "\.ph(p[3-5]?|tml)$">
SetHandler fcgid-script
FCGIWrapper /var/www/php-bin-isp-php71/user/php
</FilesMatch>
...
</VirtualHost>
PHP 7.1 config
error_log empty (not set)
log_errors on
error_reporting E_CORE_ERROR | E_ERROR | E_COMPILE_ERROR | E_PARSE