We rely on a Microsoft-provided API in order to update gamertags and construct our leaderboards. A few years ago, Microsoft stopped providing support and resources to engineers developing against their API. Unfortunately, it looks like Microsoft has now shut down the API altogether.
I don't know what this means for the future of the leaderboards or competitions, but it doesn't look good. I'm trying to get in contact with someone at Microsoft who knows about the fate of the community developer program. We'll see if anything comes of it.