I'm experiencing some inconsistent behaviour when trying to read achievements from my app. I have 3 tests accounts, 2 of which I can read achievements. However the 3rd account always returns an empty array. All 3 accounts have the publish_action permission and I've tried using both the user and app access_token. Here's the query:
https://graph.facebook.com/{uid}/achievements?access_token={app_access_token}
or
https://graph.facebook.com/{uid}/achievements?access_token={user_access_token}
Now I know the 3rd account has achievements as I get an error when I try to give it an achievement it already has and the game ticker correctly shows the achievements it has earned.