I do know this much, if the main stabilizers of the scapula (serratus anterior. Lower trap, and Sub Scap ) arent firing properly or you cant seem to get them activated properly and they are a weak as a result of this , the body will over naturally look for other way to move the scaps. It will then start over compensating and start recruiting the Upper trap and Levator scap to move the scapula. This will then cause those upper muscles to be over used and trigger points form in those muscles which can then send referred pain into anywhere all the nerve rout ( arm , shoulder , neck, fingers - anywhere along the nerve route ) and it will slowly "drag" the scaps upwards abnd scapula instability is created, and thats how symptoms and pain are caused.

If the scaps arent moving the way should be , You must re train those neural pathways and start activating the muscles that are "asleep" so to say.

Has anyone looked at the way your scaps are moving ? I know that years of gym work and to much anterior weights and not enough posterior chain work did it for me, I then re trained myself out of that and restored normal function of the scaps. And have been pain free since.

I had a minor flair up a few weeks ago which lasted a month but that was only because i was smashing the gym very vigorously 6 days a week, not stretching and well just getting back into old bad habits. The result of this was TOS type symptoms yet again, and they way i overcame this again was by stopping all the body building type trainings and focusing again on activation of the Serratus , lower trap and the rest of the posterior stabilizers.
3 - 4 weeks of physio mixed with that and i am again pain free. back to normal gym routine.

IF the scaps are the issue, then u must retrain them to work properly again or the symptoms will keep coming back.

If something else is the issue , like a extra rib or ect then i cant help anyone there. All i know i have beat this twice now and the technique that worked was neuro -muscular retraining.