I don’t know about the nerve issue, but I’ve delt with an unstable shoulder and muscles that feel like they don’t work before. Researching shoulder problems, I’ve seen that they’re often caused by injury to the Long Thoracic Nerve.
For me, my shoulder was unstable because I wasn’t contracting the “deep” muscles around the scapula that support the shoulder so the rhomboids/traps/pec can work properly. Here’s a discussion about contracting the serratus to get shoulder position correct.
Have you tried “stretching” or “traction” to open things up and try to release the trapped nerve? Something easy like this works well for me.
What about “releasing” or “rolling” the muscles around your shoulder blade that may be tight and restricted?
