It might be that you don’t have the servo arm aligned correctly. When the ROV first wakes up it tries to position the camera in the middle of its tilt range. It does this by putting the servo to the middle of the servo’s travel range, but if the servo arm is not positioned correctly, the middle of the servo travel does not equal the middle of the tilt range.
Go to the Dozuki instructions for 2.8, Guide #3, and check carefully that step 37 (centering of the servo horn) was done correctly.
If that doesn’t work, then we can move on to trying other things.