A sprung seam is the result of “springback“. It appears as a loose seam, i.e. high (loose) seam thickness, however this defect is actually caused by the 2nd operation roll being set too tight. In this case, the materials act like a spring, pushing back on the roll and “springing back” into a loose seam.
When this occurs, the correct action to take could be to actually loosen the 2nd operation roll.