Sounds like it could be a mobility issue. I have worked on getting the most mobility out of my shoulders by using a metal rod or you could use a broom handle/dowel rod to work on pass throughs.
I start with a wide grip in with the bar at my waist and, with arms fully extended all the way thru--move the bar over my head and all the way around to my back and thru again. I do this at work on my breaks and it works well. Move your hands in closer and closer for an even better stretch.
Plus during my training sesh, I will do a 15-20 min warm up with the bar going through all the movements; snatch, press, clean, squat, oh squat and snatch grip press.
Hope that helps.