unknown device - MAC hidden behind bridge

i use wifi analyzrs on my kindle to keep track of devices connected to my xfinity wifi - one of the analyzers shows a device that i'm not familiar with - while the other analyzer doesn't list it at all

the app is Analiti - and it lists a device with an IP address - instead of a MAC address it says "(now invisible due to an intermediate bridge)" - and in response to pings - it continuously says "last sensed moments ago"

does anyone know what this device is

i have identified my other devices in the list - the gateway - the firewall - and my laptop and tablets - all legit

thanks

--john