Getting 500 errors for no apparent reason

I have a client that can connect fine with the oauth and token endpoints. The problem happens when he tries to actually run a request for /users/me. These are the exact same requests all my clients run without any issue. But for his account, I get 500 errors that give no descriptive error message.

What are the possible reasons for 500 errors? This happens each time without fail.

500 errors are a bit tough as it’s an internal server error and the only way to really tell is know the specifics of the user and then check our logs to find out what might be the reason.