1) Stop Zabbix Agent on Host (Tried with 3.4 & 3.2) log enough to trigger Alert
2) Observe host being temporarily disabled in Zabbix Server Logs
Ex. Zabbix agent on zabbixagenttest01 is unreachable for 3 minutes
Ex. temporarily disabling Zabbix agent checks on host "zabbixagenttest01": host unavailable
3) Start Zabbix Agent on Host
4) Observe host being enabled
Ex. enabling Zabbix agent checks on host "zabbixagenttest01": host became available

After agent is started and it shown as being enabled in the logs you never receive an Okay message, the alert stays active, and Agent Ping shows 0.

It's not until the Zabbix-Server service is restarted that the alert is cleared and the agent ping restarts.