"Immediately" does not mean quickly so a runner who is moving slowly toward the next base is not in violation of the LBR. And technically, a runner isn't required to commit to advancing or retreating until after their allowed stop.
A runner who is in motion when the ball goes back to the pitcher in the circle does have 1 stop and then may choose to advance or retreat. A runner who is off base and not in motion when the ball goes back into the circle is required to immediately either advance or retreat and are not entitled to stoping. Once they choose which direction they are going they are committed. A runner who is on a base may not leave after the ball is in the circle. And yes, agreed, immediatly does not mean quickly.