I've had instances on the One where achievements did not initially unlock but then, retroactively, have popped. However, this is the first time I've experienced this specific error, and am not sure how it will all play out.
I am avoiding unlocking more achievements until it is resolved (more to play it safe). Initially, I figured my unlock issues were due to
Child of Light having buggy achievements (though the solutions seem to suggest most, if not all, that was patched out), and I didn't realize that I can't even access my achievements from the Smartglass or the website until I saw the achievement app error.
Not sure which thread(s) are best to monitor. This one has an official response that claims it (the thread) will be updated when more information is available:
http://forums.xbox.com/xbox_forums/xbox_support/xbox_one_sup...Posters have links to a couple other discussion threads, but the official Xbox forums are littered with various topics regarding this issue now.