Why does netxms continually try snmp communities when the community is already known ? I have a few different community strings and netxms will still try all others even though the correct string is already configured in the node settings. This causes issues with switches that have security measures to block snmp if failed snmp attemps are reached. As well as causing bloated logs with auth failed attempts.
The only situation when this might be happening - if during configuration poll device did not answer to a packet with currently stored community string. In this case server thinks that community string might have changed and starts trying all available ones. You can do tcpdump from your server filtering by device IP and SNMP port, then we will have some more information. The command is
tcpdump -s 0 -w traffic.pcap host = IP_ADDRESS
Or you can just set checkbox "Prevent automatic SNMP configuration changes" in node properties, it should prevent trying community strings.