I know this was originally an old message, but I'm a firm believer in the search function, so...
I had this when I first started pole, and then it transferred to silks. It hurt on the left, but I had a massage therapist tell me he thought it was from over-strong muscles on my right. I'm right hand dominant, and tended to favor inverting with the pole (and silks) on the right side of my body. The muscles on the right were so strong, they were pulling unevenly on the spine, making the left side "grip" to try to compensate.
To fix it, I had to develop my left side. Also, always make sure to keep those shoulders blades engaged! At the time I fixed it, I was only doing silks. I had to be careful doing anything with a split grip, including climbing. With fabric, I just split the fabric to climb (using equal hand positions) and avoided, or minimized, the actions that caused the pain.
It took a good six months, but it did go away. Now, I am very careful to work both sides evenly. I'm still right side dominant, but always try to do moves on both sides. When using a stacked grip, I make sure to switch which hand is on top or bottom.