I monitor network devices thru snmpv3 over the internet. I use authPriv, aes\des encryption and SHA authentication.

When power is lost or internet link to my network is down, the snmp devices get unavailable in zabbix. After connection is restored sometimes some of the devices don't become available till zabbix server restart. I can simulate this specially cause it doesn't repeat constantly.

When it happens I get:
temporarily disabling SNMP agent checks on host "...": host unavailable

and for some devices it's the last message till zabbix server restart. After restarting zabbix server I get:
enabling SNMP agent checks on host "": host became available
very quikly.