A device will be listed under "Unprocessed Devices Records" when we match on any parameters which already exist for a device in Device42, therefore we provide an option to merge it with the existing device or add it as a new one.
This occurs when the device matching level is Moderate/Conservative on your system under
Tools > Settings > Global Settings > Device Matching Level:
If you change this to "Classic" then delete and rediscover the mentioned device it will be not listed there anymore, as for the "Classic" case we match only by serial, UUID and hostname, if there is a match we update the existing device, if not we add it as a new device.
Please refer to this article for more information on this topic: