That is because the Spoofer is spoofing the MAC of this AP. The spoofing lists the devices that are seeing the spoofed traffic in the network. Use some sort of a wireless monitoring tool to track the signal strength of that spoofing device to get clo...

Unfortunately, the 10 second delay is expected on the Meraki Switches once they see the IGMP Leave before switching the stream. It may be worth submitting a feature request from the dashboard