Help request for a wildly misbehaving pixhawk quad - EKF errors

Hi all, I’ve just had two very hair-raising flights. Here is a FPV recording of the particularly bad section of the second one. Note the climb rate (middle left), altitude (top right) and artificial horizon all detaching from reality at about 15 seconds:

I’m flying a White Sheep 480mm quad, with pixhawk and high quality ESCs, motors etc. It’s previously flown reasonably well; although it’s never been perfectly tuned, it was stable and easily controllable. Tonight I added a cheap Banggood gimbal, and everything went wrong. Each time I put on any speed or power, I got massive uncommanded movements in all 3 axes. These eventually died down both times, but each time I struggled to manage to land it.

I have had a look at the logs, and my vibration seems pretty high, especially in the z-axis. My props are balanced, and the pixhawk is mounted in a decent bed of soft memory foam (10mm thick or so). It’s
previously flown fine like this, although I have struggled to keep vibration down. However this behaviour terrifies me, and I won’t be happy flying it again until I know what’s happened.

The logs also show an EKF error, about the time that the quad went wild. I suspect this is related to vibration, but don’t fully understand it - my reading implies that in manual mode, this has no impact on flight, only in automatic modes (where it will force a controlled landing). I was in acro throughout.

The M8N GPS/Compass module I wanted was sold out, the one I have doesn’t seem to have a compass in it so I don’t have it plugged in, and I’m using the built-in one. In acro throughout so the GPS shouldn’t matter, although it has a good lock throughout.

Full logs for the flights are here. One short hover, one terrifying flight. Two more short flights, making sure it was sane, then another lunge of idiocy.

Any help diagnosing what is going on, or advice for how to sort it, would be gratefully received!

Did you get solution for it?

One of the two IMUs in the pixhawk had failed, and for some reason the filters were switching between the working and failed IMUs.

I could have disabled the failed IMU in the settings, but I had a spare Pixhawk, so instead I just fitted it.

This trigger one more question, how to identify original pixhawk or copy of pixhawk?
Now I am doubtful for my Pixhawk 2.4.7

Pixhawk 2.4.x anything is a cheap clone. You can use QGC to check if you’ve got 2meg memory or only 1 meg