Looks to be being generated by the EmonPi, found this in the EmonHub Log:
2017-02-09 20:17:03,180 INFO my-emoncms-server sending: http://emoncms.averysradnage.co.uk/input/bulk.json?apikey=E-M-O-N-C-M-S-A-P-I-K-E-Y&data=[]&sentat=1486671423
2017-02-09 20:17:03,212 WARNING my-emoncms-server send failure: wanted 'ok' but got 'Error: Format error, json string supplied is not valid
A little while later:
2017-02-09 20:17:06,230 INFO my-emoncms-server sending: http://emoncms.averysradnage.co.uk/input/bulk.json?apikey=E-M-O-N-C-M-S-A-P-I-K-E-Y&data=[[1486671424.3045,5,303,-27,276,243.06,0,0,0,0,0,0,0]]&sentat=1486671426
2017-02-09 20:17:06,292 DEBUG my-emoncms-server acknowledged receipt with 'ok' from http://emoncms.averysradnage.co.uk
???