Are you seeing improvements with what you are addressing?
It may not be a mobility issue.
It could be a deviation in your position.
Can you have someone take a look at your positioning?
Sounds like you need to improve your shoulder position.
Another area to address the 1st rib?
Daily Rx November 3rd
Pro Episode # 43 – Pro user Request Friday: Snatch, Sotts & Torque
Jill Miller and Your Dys-Supple Neck
Seriously. Do This Yesterday. One of My All Time Shoulder Fixes

Anterior Delt Barbell Smash
The 500th Video; Great Sub-Scap Shoulder Smash Drill