Netdata version 1.13 has been broken for several months. The aggregate overview of the key system metrics has no Net Inbound, Net Outbound, Disk Read or Used Swap data showing for the EasyPieChart widgets under the System Overview section of the default Netdata page.
Inspired by this page (https://github.com/netdata/netdata/pull/5149/files/38bccf6bc016ad665a60e0adbea777b00f195b45), I installed Netdata 1.14 in /opt, modified the DEFAULT_PHYSICAL_INTERFACES list to include vmx* network interfaces and did get net inbound and net outbound data to show.
Note that the system overview easyPieChart widgets work perfectly in versions prior to 1.13 on FreeBSD.
It also does not matter whether one is running FreeBSD 12.x or 11.x, situation is the same.