Make sure that you have not repeated a top pattern, which may be cut off to fit within your block. Also check your throat space to make sure that it is not running along the leveling bar. The machine could also be coming too close to the rolled up quilt, so try rolling out a bit of space and see if the pattern quilts out completely.
Run your machine along the track to make sure the motors are not lifting off the track at the point where you are getting the line. If the machine is lifting, tighten down the stabilizer bracket if you have one.