There is a very common misconfiguration done when attempting to use SNMPv3. According to RFC 3414 (https://tools.ietf.org/html/rfc3414), each device must have a unique identifier. Each SNMP engine maintains a value, snmpEngineID, which uniquely identifies the SNMP engine.

Sometimes, users tend to set this ID to the same value for several devices. As a result, Zabbix is unable to successfully monitor those devices. To make things worse, each device responds nicely to commands such as snmpget or snmpwalk. These commands only talk to a single device at a time; hence, they do not care about snmpEngineID much.

In Zabbix, this could manifest as one device working properly but stopping when another one is added to monitoring.

If there are mysterious problems with SNMPv3 device monitoring with Zabbix that do not manifest when using command-line tools, snmpEngineID should be checked very carefully.