An unknown traffic event is noted in the web console.

Comprehensive and Detailed Explanation From Exact Extract:

When you observe an "unknown traffic event" in the SolarWinds web console, it usually means the collector is receiving NetFlow or other flow data from a device that is not currently managed or monitored in the SolarWinds database. The collector can receive flows from any device, but if the device is not added or properly monitored, the traffic will show up as "unknown" because SolarWinds cannot associate the flows with a known interface or device.