proftpd, sshd and apache processes run with /etc/init.d/its-script on linux distro.

I was monitoring 21, 22 and 80 ports with farm monitoring service: every 5 minutes service check each port and notify only failure. The failures were 5-6 times on 24h. It seems that someone kicks the switch sometimes..

I add monit and collectd monitoring and the monitoring about 21, 22 and 80 ports is every 1 minute. I do not receive farm monitoring service notify. I receive only monit notify about failure and/or succeed/changing pid number of proftpd, sshd or apache process. The failures are still 5-6 times on 24h. collectd monitoing about cpu, load average and each process is regular and there are no peaks. There is nothing kicks the switch but there is something which determines failure monitoring. is it a simple interference or is it indicative of some abnormality?

What could cause these failures?