Hello,
I run Nextcloud 13.01 on nginx and Centos 7 and was able to get the opcache warnings removed by adding the following to my /etc/php.d/opcache.ini file (below) then restarting php-fpm
opcache.enable_cli=1
opcache.max_accelerated_files=10000
opcache.save_comments=1
opcache.revalidate_freq=1