I have had chronic shoulder pain which flares and worsens and then gets better but never quite goes away since the early 1990s, just a couple years after I was diagnosed with MS. The orthopedist I saw at the time didn’t know what it was but was intrigued by the strange clicking and popping that occurred when he moved my arm behind and above me. He even brought colleagues in to witness the strange occurrence. He told me he had only seen that particular phenomenon in football players and the like from traumatic sports injury. Oh, he had me feeling so special. (Sarcasm should be noted.) He tried different massage techniques and had me do different exercises and it did eventually get better but when it came back I didn’t bother making another appointment with him.
I suppose, from reading the description, it could be ‘frozen shoulder’ with the exception that mine never goes away. Maybe because, with my MS, I now rely on my arms so much more. (Have been in a wheelchair full time since 2010.) So my shoulders never get a chance to rest.