Welcome to this board. Lots of helpful, knowledgeable people always willing to help out.
After me quilting 4-5 hundred quilts I still sometimes get puckers on the back. One I unpinned a puckered spot and re pinned it, still puckered. Just a few. It is for a grown Grandson he probably won't even notice. He has several quilts from me. I only use large safety pins.