This has happend to me , too. I call the customer and explain what I found and then I fix it while it's on the machine. All I do is loosen the tension on the quilt a little bit and stitch the seam allowance together by hand with a lightweight matching thread. Then I quilt over my repair. But I do let my customer know. It's usually because they didn't shorten their stitch length when they were piecing and the seam and the tension on the roller bars caused the seam to pop a little.