You can check the status with the command:
sh process | incl snmp
* X450a-48t.6 # sh process | incl snmp
snmpMaster 3.0.0.2 0 Stopped Wed Sep 28 06:34:26 2016
snmpSubagent 3.0.0.2 0 Ready Wed Sep 28 06:34:26 2016
Both processes should be "ready"
If one or both are "stopped" you can start them with
start process "snmpMaster"
https://gtacknowledge.extremenetworks.com/articles/Q_A/How-do-I-restart-the-snmp-process-there-is-sn...