Have you tried opening a support case for this? It sounds to me like the snmpd daemon might be having issues. Check the snmp_v2_fetcher log, also check the service_watcher log to make sure there's no daemons in a restart loop. Some basic checks to also perform: 1) license device limit, 2) hardware sizing, 3) performance tuning (bottom of AMP Setup -> General), 4) group polling (groups -> select group -> basic tab, check the SNMP version option to ensure if using v2 or v3)