I am trying to access http://graph.facebook.com/{user_id}. It usually returns all the public information about users, i. e. first and last name, gender and locale. However, on some very rare occasions, it simply returns false, there's not even an error. I have seen other questions on StackOverflow, and it's been said there that the access token may be wrong or the query format may be erroneous, but all I pass is the Facebook user id. Why is that?
Also, if it depends on the user's privacy settings, how can I enable/disable it for myself, too?
This happens if the user opts out of the Facebook platform entirely. Users can do this under Privacy Settings -> Ads, Apps, and Websites -> Turn Off All Apps. Your developer account probably can't until you deleted any applications you have created, so I would try this with somebody elses account.