Can't remove device from Connected Devices list in xfinity app

There's a laptop listed under Connected Devices in the xfinity app that has not been connected for at least a week. When I go to Device details, at the bottom it says, "To forget this device, first disconnect it from your home network."

I did that, but it's still listed as connected — even when the laptop is turned off. In fact, I wiped the system (Windows 10) and installed Linux. Yet under the device details, it still shows it as running Windows 10. However, the new system also shows up separately under Connected Devices, with the correct hostname and IP address.

How can I remove the bogus device from the list?