I am having the same problem that hasn’t gotten any better. For several months, I worked on completely letting go physically and mentally. But my body immediately tried to control the bow, but I am not sure if it is trying to control or just simply to balance the bow so that I don’t drop the bow. I have been focusing on that matter so much to the point that my tone is not that great any more when I play long tones in softer than mezzo piano dynamic while the issue persists. If anyone who has had some success on this matter, I’d love to hear the experience.