Xbox LIVE Core Services remain "limited" for Xbox One users. And it couldn't have come on a worse day: the release of Titanfall. According to user reports and Microsoft's own server status page, Xbox One owners are having problems signing into Xbox LIVE.
Though it doesn't appear the issue is caused by Titanfall's launch, the problems are preventing some users from actually playing the game, as it's primarily an online game. On the bright side, there's always the PC version which appears to be running just fine on Origin. Go figure, right?
Microsoft maintains they are "hard at work investigating the issue" but have yet to offer further detail or clarification regarding the issue.