That absolutely sucks. I have done the same with F550 builds (using DJI motors and Naza-M FC's). When flying in DJI's Attitude mode, all you have is stabilization...no GPS. It was actually my favorite mode to fly in. But it's easy to get in trouble as your inertia in flight when you let go of the sticks can run you into obstacles. Also, inertia plus wind means you really have to concentrate on what you are doing and vehicle orientation. I clipped the tops of some very tall palm trees going full out with a tail wind and pretty much destroyed my build. It's hard to watch and even harder to stomach later when you think about the time/$ put into the machine.
I feel you pain, bro. Maybe you should just pack it up and send it to a Yuneec service center for a rebuild. Best of luck to you!