[Update]: On 23 Sept 2017, we have modified our Server Agent install script to have a better Network Interface name detection (can find the GitHub commit here).
Reinstalling the Server Agent on your server now will most likely fix the issue that brought you to this article. However, on the off chance that the issue still persists, please follow the instructions below.

Old manual method of fixing the issue:

During the installation of our Server Monitoring Agent, our install script will try to determine your Network Interface name, and save it in the Agent’s settings.

However, this process can sometimes fail, in which case the Agent does not have the correct interface name to collect the network usage from.

In order to fix this issue, you will need to open the Agent script and manually set the network interface name.

Start by opening the following file with your favorite text editor:

Locate the setting called:

And modify its value with the name of your actual network interface.

Save the file, and you’re all done.

It can then take up to two (2) minutes for the network data to start coming in.