The Monitoring --> Events --> Discovery page shows me some rapid host "up", "down" and "lost" events for IP addresses that are not in use. These hosts cannot be pinged. nmap shows no services running on these hosts, either. See the attached screenshot for 172.19.96.113, for example.

According to the documentation ( https://www.zabbix.com/documentation/1.8/manual/auto-discovery ) this is not supposed to happen.