Facial bones animation stopped working

I have imported a Blender animated model (with a MakeHuman Rig) into Unity that had several animations, one of them being an animation where the model's facial bones (bones, not BlendShapes) were animated. For a month or so, this animation worked seamlessly, and a few days ago, it mysteriously stopped working.
Namely, all other animations are still working, and this particular one does move the proper bones (when I click on them in the Scene editor while the animation is running, they are changing their positions), but the model is not moving its face. This also happens in the Animation preview of the model.
I have tried changing the rig type; including these bones in the "mask" foldout; reimporting the whole Unity project; making a new animation with facial bones and none of this worked. When I baked the existing animation in Blender, Unity wouldn't display the baked Action in its animations list in the Animation preview.
All other models with facial bones in their rigs stopped following these bones as well. Everything works in Blender, however.
What can I do to fix this? EDIT: These animations work when the model is imported in a fresh new Unity project.