We have a few nodes that stopped sending snmp traps.  We've tracked this back to when we upgraded from 6.01 to v6.1. Currently running v6.1.1. After setting debuglevel 9, we are seeing this in the logs:

*********
2026.04.30 12:05:03.065 *D* [snmp.trap          ] SNMPTrapReceiver: looking for SNMP security context for node 192.168.1.4 NWS-EWG5
2026.04.30 12:05:03.065 *D* [snmp.trap          ] SNMPTrapReceiver: received PDU of type 4 from 192.168.1.4
2026.04.30 12:05:03.065 *D* [snmp.trap          ] SNMPTrapReceiver: SNMP credential validation failed for trap from 192.168.1.4, dropping
*********

Attached are the XMS server and node snmp config settings.  It's just a pretty simple snmp v1 setup that's worked without issue for years.

Obviously this is due to https://github.com/netxms/netxms/commit/272d0338b1 commit that went into v. 6.1. - previously server accepted any traps, with this is validates SNMP trap credentials.

Can you please do a tcpdump capture for the IP of that node to see what exactly community string is coming from that node.