Resolved Face tracking - Mesh not animating

I have an AR project where I am using face tracking to animate a mesh, in the same manner as animojis. It was working a year or two ago, but after upgrading Unity and the AR libraries, it now no longer works. The mesh appears and moves tracking the user's face, but the expression remains blank.

I am not seeing any errors or warnings in the console that seem applicable. How do I go about tracking down this issue and figuring out what has broken?

I have an AR Session Origin with an AR Face Manager component. I have attached the AR Face and AR Face Mesh Visualizer to the child of the face prefab with the Skinned Mesh Renderer (not sure if the hierarchy is important).

The Skinned Mesh Renderer's BlendShapes sliders all seem to move the correct part of the model.

I did try swapping in the Plasto Head asset from the Unity bundle. However that model when I use it as the Face Prefab for the AR Face Manager always winds up looking away from the screen (so that I am looking at the back of the head).

 

Turns out that during the update the AR Kit Blend Shape Visualizer on the face prefab had been removed. I must have added the AR Face Mesh Visualiser when cross referencing against the Unity tutorial. Downloading the AR Foundation samples in the end provided the clues I needed.