Flight resulted in crash

My group did our first test flight of a new aircraft that has a pretty unique design and although it flew for a little bit the flight ended in a crash. We are trying to identify the issue. Launching was done off a car launcher at 85mph and the aircraft came off smooth but immediately started to yaw to the left. The pilot gained altitude for a little bit but the aircraft began to loose airspeed then the senor dropped out, but is still contained in the ulog file. Fairly violent oscillations in both pitch and roll began and we began to loose altitude until the aircraft was landed. We took off in stabilized mode since the aircraft was moving at such a high rate of speed (stall is estimated to be 70mph) and this has worked for numerous other aircraft that we have tested with stock gains. Our running guesses are as follows:

  1. Pilot stalled the aircraft during the pitch up phase and due to being under powered was not able to regain the speed.
  2. The control loops were two far out of tune.
  3. CFD shows that the aircraft has some small moments in roll and yaw and is potentially unflyable.
  4. Control surfaces are undersized/not enough flow.
  5. The yaw moment is coming from differential thrust issues.

Will someone with more experience in log analysis and PX4 mind taking a look at the log and see if there are any blaring issues that could have caused the issues we saw?

ulog file: https://drive.google.com/file/d/1cCWO4Flspqte8iZ9W7YdRb_qWTACXfmY/view?usp=sharing
Flight review: https://review.px4.io/plot_app?log=a35d310f-97fd-4125-ac97-9050a5e0a884

Thank you for your time helping with my issue,
Dane Johnson