I did a lot with bitting the horse, letting them wear a bit while eating, which takes out a great deal of playing. Especially that gnawing on the bit while waiting around. Some do still have a little tongue or mouth issues, but the wearing of bit while eating, usually takes 99% of that away.
The one really oral horse we had, we used a loose-jaw bit on. She would stand like a rock, as long as she could lift and drop that mouthpiece. You heard tink, tink, tink, when mouthpiece dropped, but she was still otherwise. As husband said, better she has THAT for an outlet, than developing other WORSE habits for her busy-ness. I could live with the tink, tink sound pretty easily!!
Has your horse ever worn a nice medium size mouthpiece, ring snaffle to eat with? You might give it a try, see if the busy face things stop or continue. Ours usually wear the bit to eat with, then removed, over 2-3 weeks. Bit is not tight to the lip corners, nor low to hit the front teeth. Horse has to have enough room to lift it, maybe get tongue over, then back under, learn how to manage their bit with the food. Our horses get tired of chewing the bit constantly, so they learn to wear bit quietly, hold mouth still. Loose bit is better, have room to move it with tongue as needed. Can’t do that with tight bit making them smile hard.
If face movements don’t go away, guess I would just ignore it if that is as bad as horse got. Lots of WORSE ways to express nerves, so you don’t EVEN want to go there in correcting such behavior. I would not expect horse to ever be a statue while waiting around, face or lip movements are no big deal, just distracting to YOU. Might be funny if you look for it, get a winking horse!