To fully remove a device from showing in the DX Netops Portal you must remove it from all Data Sources that are providing it to the DX Netops Portal.
For example, if you have Network Flow Analysis (NFA) and the Data Aggregator (DA) providing a device to the Netops Portal, if you delete the DA entry in Monitored Devices, CAPC will continue to show the device because NFA is still syncing it to the DX Netops Portal.