(by AO3 user scratch is the best): For the curious, the reason this happened is because someone placed the two billionth, one hundred and forty-seven millionth, four hundred and eighty-three thousandth, six hundred and forty-seventh bookmark on the site. That's the largest ID that can be stored in a tyoical database column. To fix it they have to migrate the entire database to use a different type for bookmark IDs. Except, of course, this will take a while, because there are two billion of them, lol. Good job, guys. You used all the bookmarks. There are no bookmarks left.