I cannot discover any functional or mechanical problem in the log. The the aircraft follows the controller outputs (even during the oscillation; with the usual phase delay of course) so the motors seems to be fine. And the controlller reaction seems to be fine as well.
The clipping during the strong oscillation could be physically correct, excited by the the bang-bang motor dynamics. I can imagine such values even without any mechanically loose components.
By looking to the gyro signals and the rate controller it could be a ‘simple’ closed loop oscillation because of too high rate controller gains.
Maybe is this drone family is ‘overtuned’ , and has too low stability margin on the rate control loop?
Then most of them are flying perfect, but in the case of some tolerances and other circumstances oscillations will occur. Were the rate gains tuned for an empty or fully loaded vehicle? How much were they reduced after that?
For a 25kg vehicle, the rate control loop performance looks for me too good before the oscillation. If it is on the performance limit, then only some circumstances are needed and oscillations can develop: assymetrical motor loads combined with the current load case, sloshing fluid, and… and…
The oscillations are leading to saturations (motor 1, 2 are alternating on minimum), and even more phase delay.
The lower motor load on 1 and 2 could be one of the main factors in this case. As it was already written, check the motor angles. One or more are possibly tilted and causing yaw moment. Then try to tilt back until the sum of CW motors has the same load than the sum of CCW-s.
But, as this is mostly the case, this is just a hypothesis. Just one possible cause for the crash. I am not convinced, but in your case i would reduce the rate gains just to be sure.