Actually, I had a frozen shoulder some years back, I was a bit silly and suffered with it for about 3 years before I went for treatment.
The shoulder is a complicated setup, My Osteopath diagnosed some damage and that had resulted in some muscles working a bit harder to compensate for the injury.
Those muscles became stronger than the original injury connected ones, which weakened through being used less.
This caused imbalance, & had the effect of putting my shoulder out of it's normal position and resulting in ''clicking'' and severe pain - i.e. frozen.
I had to strengthen those weaker muscles with exercises using Latex as a "tension pull".
It took around 3 months to fix it correctly.
The problem is if it's not diagnosed correctly in the first place - it takes forever to fix it!