Firstly, I'm not a qualified medic or anything, although I have studied sport science and physiology etc.
It could be related to your scar tissue, it does, however, sound more like a nervous issue - if it feels like tiny spasms in your cuff or as though something is tugging away at small areas of the shoulder, then there may be nerve damage or some synaptic short circuiting.
It could be permanent as a result of the damage, or it could be a temporary issue helped with continued rehabilitation.
I'll stress again that I'm not a med, but I do hope you'll find the info useful