"Error Streaming Data" appending to end of JSON response

I am getting a few hundred thousand records per some unit time fetching around a minutes worth of data at a time.
Maybe once every three days or so I get a JSON response along the lines of

(a few thousand JSON records)
{the last JSON record ..."WorkerSubrequestCount":0,"ZoneID":277273}
Error Streaming Data

The 'Error Streaming Data' is outside the JSON blocks and just tacked on to the end.
Any idea what it means and how my code should respond to it?

At the moment if I get a response with that string tacked on the end, I toss the block and ask for it again.