I'm not sure but I had something similar. I had one shoulder forward and left shoulder higher and back, leading to bend in spine and all kinds of unsymmetrical difficulty. The only succes I had was to work both sides of my trapezius and rear shoulder gently at first with bands held in both hands, rowing movements daily, in various small to larger extrended movements, and then yoga back exercises to correct the spine. It took a very long time, to bring the body back to finding its normal balance, and then a long time convincing me that normal was normal.

Muscle spasm, or unused muscle takes a long time to convince to remain switched on, and using very light resistance initially is the best way for me, so I did alot of taichi. What I found was that if unopposed by the right side my left traps would pull the shoulder all the way back. Its only the balance of both sides that keeps the shoulders equal. So I had to be extremelyt particular at working muscles in a symmetrical way. Not using one side alone for a time. The same applied to working the chest shoulders and traps.

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