Unstable behavior big hexacopter

Hello. I’m working at project of a tethered hexacopter. At last test i’m try to measure current during flight. I’m fly with plywood sheets simulating the wind load of the cable. Everythig was OK, until moment when i load drone by 37kg flight mass. strong vibrations occurred during acceleration. And the MP issued messages: EKF Primary changed: 1, EKF3 lane_switch1, Failsafe vibe-1, vibration compensation on. At this moment i almost loose control on drone, and land it immediately.
Can you help to to determine reason of strong vibrations in flight? Or may be it’s other reason of bad flight behavior?
Flight logs: Last LOGs hexa — Яндекс.Диск (from 14:33 to 14:35)
Video: GH016487.MP4 — Яндекс.Диск (from 4:30 to 5:35)

I think this drone can be tuned better. Look back in your log, I see something:
. This is a hex so basically, PID of roll should be different from pitch (ATC_RAT parameters)
. Behavior of ATT.Roll, ATT.DesRoll, ATT.Pitch, ATT.DesPitch is not so good
. You have a strong vibe on IMU0 - around 30 which should not be. Being less than 15 is standard. In the IMU1, vibe is much worse. I think you need some dampers or so

Hope these help.

Thank’s for this. I think dampers can help decrease part of vibrations.

One more thing I forgot to mention in the previous post, I saw INS_GYRO_FILTER and INS_ACCEL_FILTER are 20, it is a bit high for this large drone, try to reduce them a bit following the tuning guide.