I've been having a problem since day 1 with Zabbix of host going down, then coming back up and then not reporting that its back up. This always happens when one (or more) of our sites go down with multiple host for any reason, be it a blackout or a site upgrade. For example: 10 host go down at once, 8 come back, but 2 will just state that they're still down. It doesn't matter if I go onto the host and restart the service either, I HAVE to restart the entire host to get it to register that it's not down anymore. This needless to say, is kind of a big deal when my monitoring software can't even be bothered to tell if a host is up or down. How do I stop this from happening?