FB.getLoginStatus does not fires callback function
I just had the same problem, though it only happened to some users.
I finally found out that if your app is sandbox mode, none-developer users can still see your app as a pagetab. But calling getLoginStatus will fail silently (even logging turned on).
Took a while to figure that one out, I hope this can save someone else some time.
FB.getLoginStatus
does not fire the callback when you are running the website on a different domain than the one that you registered the app with. I usually find myself in this situation when I am developing locally or on a staging server.
For example, if you registered the site with example.com and your staging server is example.mystagingserver.com, the callback wont fire. In this case, you need to create a second application in Facebook and use the Application ID and Secret for the new app.