Output Port of an inner process group has high CPU utilization when there is backpressure

Related to the template that drew out the issue with DistributeLoad in NIFI-1269, noticed that the computer was working fairly hard despite backpressure throughout the system effectively stopping processing/ingest.

After going through the system, it seemed this was related solely to the output port of the process group. Toggling this directly went from near zero cpu usage to a much higher level of consumption.

Will attach a template. To recreate, have the entirety of the processing path get backpressure to the point of ingest with GetFile. At this point, all components can be stopped. Toggling the Ingest File Stream output port will show the high level CPU usage.