This will happen if the device name was previously set under "Physical & Virtual" in the NFA Administration GUI:
Once you make a change to a device name in Physical & Virtual, that will override whatever name information we get back via SNMP.
Please go into Physical & Virtual and search for your device. Select your device and click "Edit". Do you see a "reset" link here? If so, that means that there is a value already in the database that is overriding whatever we get back from SNMP.
You can either manually enter the new name here, or click the "reset" link and try doing a new SNMP poll instead.