I found these errors today in my the cron log : /var/log/cron

 May 10 09:53:01 sysadmin CROND[2267]: (librenms) CMD ( /opt/librenms/alerts.php >> /dev/null 2>&1) May 10 09:54:01 sysadmin crond[63]: (root) BAD FILE MODE (/etc/cron.d/librenms.cron)

I wrongly assumed a 755 permission was needed for crons, seems I was wrong. For cron execution we only need 644. Surprisingly the issue gets resolved then and cron does execute the cron. I believe this is new behavior in from Centos 7.

Chmod to the solution :

chmod 0644 /etc/cron.d/librenms.cron