Zabbix has consistently failed to send alerts due to collection issues.
Zabbix server also stops collecting the data, generating the error of "Zabbix agent on {HOST.NAME} is unreachable for 5 minutes" in the collection machines, after a time zabbix itself recovers Usually, other times we have to restart the zabbix server service.

The graph shows "no data" and after a certain amount of time (an average of 5 minutes later) it fills the graphic of the missing data and re-collects when the collection returns automatically, when manual restart, the graph is no longer filled and all collection data is lost.

This error happened after a migration from zabbix 2.4 to zabbix 3.2

The housekeeper is disabled, even with the housekeeper enabled the problem continued.