Dozens of Unknown Devices

Check to see if the MoCA feature is enabled in your gateway device. We've seen many posts here that the MoCA feature gets turned back on with their overnight re-boots / updates for the device. You should use a MoCA P.O.E. (Pont Of Entry) filter on the coax line like this one:

https://www.amazon.com/SNLP-1GCW-Filter-Eliminate-Multi-Room-Interference/dp/B07SLD9QPH  

It will block the neighbors' MoCA signals from affecting your network.

If you are not using it, disable it. Not sure if this still applies. YMMV. To disable MoCA on your device go to the gateway login http://10.0.0.1 

Default login info is:
Username: admin (all lowercase)
Password: password

Once in you will find the drop-down on the left of the screen that is labeled “Connections”.

Click the drop down---> click MoCA---> right side of screen click “disable”---> save changes.

Hey @user_56dd3c,

Thanks for visiting our official Xfinity Community Forums support page. Please accept my most sincere apology for the experience you have encountered.

@EG provided some great and helpful information. With devices connecting via MoCA, you may not have a MoCA POE Filter in place causing some unknown devices to connect.

I would highly recommend visiting a local Xfinity Store where they should be able to provide you with a MoCA POE Filter that you can easily install. Once installed, you can remove the devices from the Xfinity App. 

You can find the closet Xfinity Store by visiting our Xfinity Retail Store Locator and Service Center Locations page.

If a Comcast store isn't convenient MoCA PoE filters are like $10 on Amazon.

I'd say if you can disable MoCA on the gateway do so until you can get a filter and just put up with any MoCA devices you have not working until your filter shows up.  Your MoCA devices if you have any might keep working off a neighbor's internet connection, so check for that too.  MoCA is really rather lacking in security and that filter really needs to be there.

If you have the comcast wifi router people can piggy back on your internet with a comcast login. I don't have that issue since I have my own router.