Side "Caves In" When Doing Shoulder Press or Raising Arms in Front

I started noticing this while doing shoulder presses, which I normally only do once a week at the moment. I also notice this when raising my arms straight out in front of me, or even 45 degrees. It’s only my right side that feels caved in to some extent. What could this be? Can someone give me a rundown of what’s causing this, and how to go about fixing it

Can you please elaborate on what is happening or perhaps link a video or photo?

whenever I raise my arms up in front, or at least 45 degrees, my right side doesn’t feel it’s functioning or moving the way it should compared to the left side of my rib cage.

This still isn’t any clearer. Please elaborate on your original point. What does caves in mean? what exactly doesn’t feel right? Whats going on at your ribs?