Xfinity App on Apple TV 4K will not allow me to watch live sports while Apple TV is ethernet connected to Comcast [Edited]

Thanks for letting us know! It's likely you're receiving that error because live sporting events are very particular about verifying they're being broadcast to anyone's home correctly. In your case, the error message you're receiving is not incorrect in that some programming does have to be viewed exclusively via a Wi-Fi connection to be able to verify you're using your home network. When you're connected via Ethernet, the Xfinity app/Apple TV has no way to tell what Wi-Fi network it's connected to to relay to the Xfinity app for authentication when sports are on, so it pops out that error. Does the programming work fine when the Ethernet is removed, and it's connected to Wi-Fi only?

@XfinitySeth​ I’m not going to disconnect the ethernet cable on my AppleTV 4k.  It’s buried in an AV rack.  

The xfinity streaming app can determine if it’s connected to a Comcast network via ethernet or WiFi! The app can simply perform a traceroute to determine if it is traversing a Comcast network. I’m a network engineer and a software developer. This is simply lazy programming by the Xfinity stream app dev team. 

I understand not wanting to mess with your setup as is, but it's not a matter of detecting a Comcast network, it's a matter of detecting your home Wi-Fi network specifically, which is going undetected if the Apple TV is using the Ethernet connection. The sports programming requires specifically a Wi-Fi connection, so those errors you're seeing are by design as we have to adhere to broadcasting regulations for these live events that require we verify how the program is being watched explicitly via Wi-Fi.