The bug has to do with blender 4+ and diffeomorphic rigs. The tutorial is in the rar file, it's a 12 min video sped up to 3. The bug derives from the scaling of facial bones. Blender 4+ for some reason turns the scaling down to 0. You need to delete drivers and scale them all manually back to 1. Also, check the parent bones, like the main upper/lower face bone, head bone and their constraints, because they might have a "copy scale constraint" of a bone that its scaling is also 0.
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