What version of NetXMS do you use?
Any object that is added to NetXMS should be shown in object tree. Have you tryed to serach in using object tree filter IP address search like: ">10.5.0.27"
PS. May be connected https://www.netxms.org/forum/general-support/ip-conflict-with-deletedchanged-node/?topicseen
Then NetXMS server cannot match it to correct device - there are just no enough information. You can setup syslog proxy on agent behind NAT so it will receive syslog messages from original addresses and forward to NetXMS server.
Best regards,
Victor
