Do you have any recorded results stored with the manager object? From the docs:

Use this method to asynchronously query for tremor results recorded by the monitorKinesias(forDuration:) method. The movement disorder manager keeps tremor results for only seven days after the time of recording.

It sounds like you're authorized, and have correct entitlements, but I wonder if there's just no data recorded yet and you need to call monitorkinesias before attempting to get the results.