Some Xbox One owners who use Comcast as their ISP are unable to play games over a WiFi connection due to an ongoing bug with IPv6 network addresses. The company is currently working with Microsoft to resolve this issue and recently posted a status update on its support site.
Comcast and Microsoft are aware of a software issue affecting the ability of Xbox One users to play some games online. This issue is only observed when the Xbox One is connected to a network via WiFi and when that network also has an IPv6 address. In those conditions online gameplay for some titles may not work.
Until a viable fix becomes available, Comcast customers can use a wired connection as an alternative for online play.
[via Comcast]