I'm not sure I can help but I'll offer one suggestion. Do you spritz your seams with water or use a steam iron to press your seams? Like NJ Quilter, I use copy paper. I had a center seam that wouldn't lay flat so I spritzed it and ironed it; it puckered. Not sure if it was fabric or paper that puckered but now I wait until I remove the paper and then spritz and press those seams again to get them flat.