My problem was very recent as well. See previous post. This seems to have resolved it for me on a Surface Pro 4 with Windows 10 fully updated.
Via device manager, system devices, I updated each the drivers for each of: Microsoft camera, front camera, and back camera. Each time it said that I had the current driver. Then I did a shutdown (not a restart) followed in 30 seconds by a start. This time the Windows Hello function with the camera face recognition worked. Problem resolved.