I am using the 32bit Basecam Alexmos gimbal board. My gimbal works completely fine in the roll and pitch axes. For some reason though the yaw axis is constantly shaking around and says motor is missing steps. It shakes back and forth and it never stable. It's for a mirrorless camera and the motors are T-motor GB54-2. I have tried the following to fix it.

1. Swopped the pitch and yaw motors around. Exactly the same problem still occurs on yaw axis only so it's not the motor that is broken.
2. Changed the outputs on the board so that the yaw output is for the roll axis and the roll output is for the yaw axis. The exact same problem is still there, therefore it's not the motor drivers.
3. Tried every single combination of PID settings for the yaw axis. I've also tried attuning the yaw axis, but the same problem happens.
4. I've tried increasing the power to the yaw to the maximum and nothing happens.

The gimbal is completely balanced. The motors are definitely powerful enough for the camera. There is a camera IMU and a frame IMU above the yaw motor. All the IMUs are fully temperature calibrated and show the angles perfectly on screen.

Has anybody had this problem before and know how to fix it? I feel like I've tried everything and it's never going to work.