I forgot to add some details:-
Pixhawk PX4. The gimbal tilt is on RC11, roll on RC14. I've noticed that with the latest firmware 3.52 that in the full parameters list there is no longer a parameter for RC_FUNCTION, so how is now possible to set the correct function.
I know that the gimbal operates correctly, having checked it directly from an Rx.
The camera trigger function still works correctly.