Does my demo scene work on your side ?
I see that your camera is too much zoomed in and gets below the ground, so the camera cannot detect the terrain below it. the X angle is really low too, the camera is supposed to be always on top of the terrain, looking downward.
You also have cliffs which makes it hard for the camera to work with and that creates a jittering.
The terrain module is just a helper to adapt the ground height property of the camera. It does not include a collision system to avoid obstacles and cliffs.
So my advise is to delimit bounds for the camera, so it does not go too far (inside the cliffs). and to play with the min pitch angle, and min distance. If you're looking for a camera that avoids obstacles, this is not the purpose of this plugin, you will have to implement that part of top of it.
I hope that helps!