So this is likely happening because the size of the returned result is exceeding the memory available to the service that packages the result. The service crashes, so the HTTP request returns a failure. We are looking at ways to address the root problem. In the meantime, can you please:
1. Identify who you are so that we can work with you to design a query that will run successfully
2. Tell us what query you are trying to run (we think we know the submitted query that caused the crash, but would be good to know directly from you).