I think I may have found the issue. It’s a result of the password reset thing from back in March. Those who never changed their password since the reset, aren’t able to login to Twitch applications. The API should be a little more clear about this and return a proper error rather than a false user with a bunch of “e” information.
I’m not 100% sure that this is the issue, although some people have said that changing their passwords made it start working all of a sudden. So I have a very strong feeling that it is.
Edit: Okay, people are still getting errors. The API is no returning nothing at all for the user.