While running calculations, I find that some records have theirerror field set, even though thestatus field does not indicate an error. Some arerunning and others arewaiting. In all cases the value of theerror field is

{'error_type': 'unknown_error', 'error_message': 'QCEngine Unknown Error: Unknown error, error message is not found, possibly segfaulted', 'extras': None}

What does this mean?