Cube Black crashes in extreme roll and pitch tests

I have been testing my drone mounted with black cube and arducopter 3.6.8. After some initial tests and some manual tuning, we went on with doing the autotune. Later after completing the autotune the quad was quite stable as compared to previous tests. But when to test the maneuverability of the quad we did some aggressive roll and pitch actions. Eventually quad was unable to perform those moves and crash landed. We are unable to solve the issue please help or advice.

Please find the log here.

Link to log is dead. Possible fixes without seeing anything:
Esc desync(props too big or heavy and motors can’t stop/accelerate them fast enough)
Poor tuning of PIDS under bad weather?
Changed configuration compared to autotune?(all up weight, bad CG, insuficient thrust)
Too much movement required for that airframe(trying to drive a bus like a ferrari…)