Puckering.

Puckering is cloth pulling up into ripples around and inside a design, because every needle penetration draws the fabric toward the stitch line and the stitches then hold it there (Wilcom EmbroideryStudio help). On the machine you usually cannot see it. The hoop holds the garment flat and the backing is still full size, so a piece that will ripple later can still pass the operator's look. Some of it shows the moment the frame comes off, and the rest waits for the customer's first wash, when a cotton knit relaxes and shrinks around a design that cannot shrink with it. Every cause sits upstream of that wash: fabric hooped under tension, backing too light for the stitch density, missing underlay, no pull compensation. Nothing can be repaired, because picking stitches out of a knit leaves the holes behind, so the bill is a replacement garment for something the customer has already worn.