Phantom 4 Pro yawing to left during mapping missions

My P4P is yawing during mapping missions.  It seems to always yaw to the left.  The actual flight path stays straight because it is an autonomous mission but the bird is rotating left and it should not be.  I have calibrated the IMU and compass with no luck.  There are threads out there for guys doing video shoots who have the same problem but since they are flying manually I would imagine they deal more with it drifting off course.  My problem is that the photos are rotating during the flight path.

If anyone has delt with this problem and knows how to fix it please let me know.  And to be clear, the whole drone is flying in a yawed position.   The problem is not a yawed gimbal. In the photos below you can see that it started straight but continued to yaw left as it flew.  I have had the problem in both Pix4D capture and Map Pilot so I am confident it is a bird side problem.  Any help will be appreciated.


In the linked photos, it flew parallel to the street and the building.  You can see the yaw get progressively worse.  There are 2 recent days of flying.






I swapped controllers out and it seemed to be the same so it is not a controller issue.  And if it was it would yaw to the same side each time.  I flew multiple cooridor missions (using Map Pilot) so that I could follow the road and view it turning.  It was turning to the West.  So flying north, it turned to the left, and flying south, it turned to the right.  

What I have not had a chance to test is what is it doing when flying a long straight line east and west.   I got another P4P because I had to have a good one to fly and hopefully I can figure out what is going on with this one that is giving me problems.  

This is not an app problem.  This is a P4P problem.  Because it happens regardless of the app.  When using Map Pilot (for the purpose of following a long street), when I manually straighten up the P4P to be parallel with the street, the “arrow” on ipad screen that indicates which direction the P4P is pointing, was now pointed at an angle (when the P4P was actually turned straight/aligned with the road).  

I have to believe this is a compass problem.  But calibrating the IMU and Compass multiple times has not solved the problem.  So I really don’t know where to go from here.  

Tony, I am just thinking out loud.  If it was a compass problem, then it would not fly to the correct destination waypoint.  The P4P is flying to the correct destination waypoint.  It just simply yaws along the path (the futher it travels the more it seems to yaw).  So that makes me think it is not possible to be a compass problem.  If it was, it would fly off course all together.

I have no idea if a problem with the IMU could cause this behavior.  If so, I have no idea on how to fix it.  Let me know if you have any thoughts.