I already said in the O.P. they appeared to be at 300'-400', " low enough that if I were flying a drone I'd have been concerned " is how I put it and thats an easy guess to make since I know what a similar size aircraft looks like flying low and...
No-one can read what you wrote, the way you posted it.
I can see that you put in a lot of effort so I've formatted your unreadable mega-sentence into semi-sentences, so others can read it.
Nothing has been changed, only some spacing added.
here...
That sounds like it could have been a reinforced concrete surface?
... which could be the source of the magnetic interference.
The first indications of the collision are in the pitch, roll and yaw data from 11.9 seconds.
But the compass starts...
Could you post the recorded flight data which DJI would have examined?
There's no guarantee that it will have the answers, but it might be of some help.
There are a couple of options ...
1. Go to DJI Flight Log Viewer | Phantom Help
Follow the...