Question Problem with AR Foundation face mesh

I followed this tutorial to get AR Foundation to make a face mask: https://tutorialsforar.com/face-tracking-using-arkit-and-ar-foundation-with-unity/

It all compiles and runs on my android phone (S20+) but it only draws a small part of the face mesh? Just the edges of the face, nose etc? If I turn my head it draws the sides but not the front? I've also tried not drawing the camera image and it's the same problem.

Any ideas why this is happening? I've tried several different phones but all have the same problem.

Screenshot from the app attached, it should just be a magenta mask over the full face. But you can see the small slices of purple.

 

it kind of looks like the mesh is inverted (backwards)?
that color usually means shader is missing or has error, can check device log for error messages:
https://answers.unity.com/questions/492681/how-to-use-adb-logcat.html#answer-571021

this project has face mesh also, maybe it works:
https://github.com/Unity-Technologies/arfoundation-samples

 

This thread had the same issue:
https://forum.unity.com/threads/arfoundation-ar-face-reversed.1067966/