Logfile randomly gets -1 -1 on top line

Jay Hennigan <[email protected]> Sun, 14 Feb 2016 18:32:46 -0800
Newsgroups gmane.network.mrtg.user
Message-ID <[email protected]>
Running classic MRTG version 2.16.2 and at random times some targets 
will stop updating. When this happens, the top line of the logfile has a 
pair of -1 values.

Any idea what the cause is and a possible fix? It looks like this:

1455503095 -1 -1
1455503095 0 0 0 0
1455502518 0 0 0 0
1455502500 0 0 0 0
1455502200 0 0 0 0


--
Jay Hennigan - CCIE #7880 - Network Engineering - [email protected]
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV