I think your problem is you don't have the check valve assembly on the circuit. in 2016, JD removed the checks from the Reel f/a valve on the combine, and installed them on the header instead. They did this to reduce the oil leakage at the single point, but it has caused a huge MESS for everybody else. Any pre-2016 header connected to a 2016-> combine now needs a check valve assm. added to the header. And 2016 -> head installed on an earlier combine needs one of the checks removed, either the head or combine (and whos going to know down the road....)
The symptom of "no check valve" is the reel f/a or deck plates just "drift" there is no check to hold it in place. So if your reel is down, its going to just slide forward and out along the arms...
The check valve update bundle for a 2014 640FD is BXE10697