You might have added more devices to your network and may therefore need to forcefully discover these devices. You can discover such devices on demand by following the steps below:
The device is discovered and classified properly.
Alternatively, you can also add devices to a specific category directly.
Note: If you are unable to add the device or if does not show up in the map in which you are looking for, try pinging the device from the OpManager machine and check for response. Search the device using the Device Search box on the top right corner in the WebClient.