In order for entries to be added to the SNMP Trap Log, the SNMP Trap Listener must be enabled. For more information, see Enabling the SNMP Trap Listener.
Additionally, if the trap receiving port is not on the firewall's list of exceptions, traps may not be receivable, and as a result, will not be added to the SNMP Trap Log. Please ensure that the trap receiving port is on the firewall's list of exceptions.