This sounds like another manifestation of a bug which has been discussed in many previous threads.  V4 will lose parenting of hair and/or jaw parts if you have PointAt invoked for the eyes.  Locking the actor doesn't solve it.  You may notice that if you go to the frame you want and change the camera (e.g., go from Main Camera to Face Camera) then rotate that camera, the hair or jaw will snap back into place; but if you then go to another frame the parented parts are at that new frame's position.  Try turning off PointAt if you have it invoked for the eyes and see if the issue disappears.