Large octocopter pitch up on landing leading to a crash

Hi all,

I’m flying an H configuration 35kg octocopter, with 32’ props, Tmotor Alpha ESCs and Cube Orange.
The drone has been autotuned in all axis, the vibrations are minimized and, although it needs more tuning to achieve the locked-in feeling, it feels decent.

The problem is that when I land (in loiter mode) with a low rate of descent the drone lands and then after a second pitches up without any RC input while the throttle is minimum. This behaviour has happened a few times but as soon as the operator changed to Alt Hold the drone settled down and disarmed.
On this occasion, the operator added full throttle right after the drone pitched up which made it flip backwards and braking most propellers.

Please have a look at the log file here.

I want to ask why the drone can pitch up without any command.

Is there a way to automatically set the Land mode when the lidar detects ground at 2m and the throttle stick is down?

The log link has an access requirement.

Sorry for that, please try again Log - Google Drive

Has anyone seen the log? This might be an important issue to look into since it happened both in 4.0.7 and now in 4.3.5. The only reason I do not try to replicate it is the high cost of propellers.

The only reasonable explanation I can think of is the braking manoeuvre in Loiter mode in combination with a soft touchdown (so the copter will not know that it has landed).

Would that be a possible explanation?