i’m having the same issue with the Mavic three Pro and it’s right out of the box. I had that issue with my past Mavic three pro and I sent it in for repair and they just sent me a new unit and a new controller and it’s doing the exact same thing...
Gimbal drifting upward randomly during flights and when tilting the camera upwards or down. This started a few months ago on my mavic 3 Pro of which I've had no issues. I update firmware to drone and controller regularly and never have issues...