FreePBX 13.0.124: Network Statistics, impossible value on restart

I am running FreePBX in a virtualised (ESXi 6.0) environment and using vmxnet3 devices. This may, or may not, be relevant to this issue.

If I look at the “FreePBX Statistics - Network” for a period that doesn’t include a restart of FreePBX things look quite normal.

However, if I look at a period that involves a FreePBX restart then I get what looks to me like totally impossible information. (Note the scale on the RHS of the graph!)

If I hover over one of the large green columns with the mouse I get a text that says: eth0: 8796093022174

Does anyone know:
a) How to stop this happening (assuming it isn’t a fundamental fault in FreePBX)?
b) How to remove these from the stored data so that the graph is useful?