I'm having similar issues and it seems like normal stretching is not doing anything to help.. I have to keep my hands very wide on the bar and it feels like my arms start to go numb on higher rep sets. I also can't scratch a large portion of my back. I'm open for any suggestions.
I've been trying to do static stretches held for 2 sets of 20 seconds, I do the one where my arm is against a wall and I rotate my body. Is there something else I should try? More sets, more time?