Big Y6 hexa hard landing

Hello community,

I’ve been developing a big hexacopter in Y6 configuration for a project. We’ve flown about 9 hours in total and covered almost 100 km with the hardware. While doing some operational testing we encountered weird behavior where the drone would reach a setpoint and kind of lose itself, do a turn and then start descending. It did this twice prior to this hard landing on two earlier flights (same day) but recovered quite quickly. For this reason I did not intervene with the drone during the descent, giving it the benefit of the doubt that it would correct itself. Sadly it did not and I had to intervene, I brought the throttle up to 100% but did not manage to safely land it, the drone just kept descending.

The log is here It seems to be an IMU error and my hypothesis is that we’ve used up or flight controller.