Mouth cavity strange animation

My mouth cavity is animating in a strange way. (I hid the skin mesh so you can see it more easily)

The opening at the front is where the mouth cavity joins up with the face skin - the opening at the front follows the lip movements (generally correctly). But if you watch the video, the back part of the mouth cavity jumps all around the place, including through the skin of the character at times.

Is there a reason for this, or a way to stop it from happening?

image

Here is an example of some of the blendshapes being generated.

Can this be due to the mouth cavity being too close to other parts of the face, e.g. under chin?

So you think it is proximity of the mesh vertexes with other meshes being animated by audio2face? My goal is to keep the vertexes near the front of the cavity moving, but the ones at the rear of the cavity I want to get audio2face not to move (by making sure not close to other things).

There are some challenges there - the quality of the mesh is not great at times. E.g. the teeth and mouth cavity might be intersecting.

I cannot easily change the meshes individually (they are generated by another tool, and I am trying to simplify the process for everyone using that tool). I can however write automated scripts to do things to the meshes (I have had to write Python code to rebuild the meshes to remove unused vertexes already). Are you suggesting sloping the rear of the mouth cavity up might help? (E.g. add a bit of a Y boost based on the distance from the front of the cavity mesh.) I can try that. My alternative was to try and splice the mouth cavity into two meshes and only make the front mesh dynamic.

It’s hard to tell for sure what the issue is without looking at the scene. But I assume there’s something wrong with the deformer bindings.
Another way is to find the culprit deformer and set the weights its problematic vertices to 0.0