...
Edit the /tmp/mx1_lon_uk_traffic_in_20683.rrd.xml and find the offending data. As we know the data is in the order of 10e11, we can search for the following string e+11. We can see the timestamp is in the right range.
NOTE: The values in the RRD file are in bytes per second. You will need to multiple these values by 8 to obtain the bits per second. The graphs on the website and CSV files that can be downloaded from the website all show the traffic levels in bits per second.
Inbound traffic:
<!-- 2016-01-18 00:00:00 UTC / 1453075200 --> <row><v> 3.5642652369e+07 </v><v> 1.1136736365e+06 </v></row>
<!-- 2016-01-19 00:00:00 UTC / 1453161600 --> <row><v> 9.0115656678e+07 </v><v> 3.1514951986e+06 </v></row>
<!-- 2016-01-20 00:00:00 UTC / 1453248000 --> <row><v> 3.8543163654e+11 </v><v> 9.2684560857e+09 </v></row>
<!-- 2016-01-21 00:00:00 UTC / 1453334400 --> <row><v> 8.0043154538e+07 </v><v> 2.7647348898e+07 </v></row>
<!-- 2016-01-22 00:00:00 UTC / 1453420800 --> <row><v> 1.0178635224e+08 </v><v> 2.1954640988e+07 </v></row>
<!-- 2016-01-23 00:00:00 UTC / 1453507200 --> <row><v> 6.5086071137e+07 </v><v> 2.7845010247e+07 </v></row>
...