Update: Microsoft have reached out with an official statement, below.
We are aware of issues some players have been experiencing with matchmaking and we’re working around the clock, alongside the Xbox Live team, to improve the situation. We have deployed an update that has shown some improvement, and we continue to optimize the experience. The update deployed to matchmaking was done on the server side and does not require an extra download to your Xbox One. This is our top priority and will keep everyone updated regularly as we deploy continued improvements.
Halo: The Master Chief Collection is one of the biggest launches for Microsoft’s Xbox One this year, putting together all four Halo games featuring the series’ icon for players to experience his story again, or for the first time. That’s not all though as Halo has had some of the most memorable and addictive multiplayer in any FPS, and many people would have bought the collection to play that again on the new generation. However, the collection is suffering from launch day issues with players unable to connect to any matches. This has led to Microsoft putting up a service alert.
Xbox members, are you having a tough time matchmaking in Halo: The Master Chief Collection? As you read this message, we’re working with our external partner to correct this issue right away. We appreciate your patience in the meantime! We’ll update you again when we have more information.
In this day and age it isn’t unexpected for games to suffer from launch issues on the multiplayer side of things. Hopefully for those of you who have the game this will be resolved pretty quickly. There’s also another service alert though unrelated to Halo. This one is instead regarding donwloading purchases, which has been on and off for the last couple of days.
Are you having trouble when trying to access content from the Atlas Digital Content Pack for Call of Duty: Advanced Warfare? Are you having issues trying to purchase Tokens for Project Spark using the Windows 8.1 application? We are aware of the difficulties and our team is hard at work trying to get everything straightened out. Thank you for being patient while we work. We’ll have an update for you as soon as we have more information.
Let’s hope that gets sorted out soon too.
Source: Xbox Live Status Page