Pixhawk clone killed my plane. Or what?

Hi all!
Long story short: pixhawk (clone) 2.4.8; i was flying my x6 wing in strong winds; cruising was ok, switched to fbwa - ok, switched to manual - nose dive without control, switched to fbwa - still diving, switched to cruise - still diving and… crash :frowning: After the crash both servos ok, wings and elevons - ok.
I analized the log file and discovered that during the final dive the pixhawk was not even trying to level up the plane (servo outputs were in about neutral position). Unfortunately this was the maximum i have understood from logs :frowning: Could anyone help me understanding the real reason. I have also attached the video from my ground station.
Thank you all in advane!

Log: https://yadi.sk/d/67wc_T57ucemN
Video: https://youtu.be/-EEGsMoJ02g?t=645

PS: my airspeed sensor and voltage/current sensors were not callibrated - their readings can be ignored