Tracking transform position

So I have a script that takes the enemy and moves it between its starting position and the transform position of another hidden game object. The script works fine for the movement. However, I want the script to only run if the player isn't seen and then resume playing once the player is not seen once again. I have it tracking the location, but when I switch the bool, it jumps forward like the script was still working even though that code should not be running anymore due to the flag being set. I want it to stop and resume from the same place, but I'm hitting a wall at figuring it out. Code below:

 #region Notes Section
 /*
 
 Author: Paul Christopher
 Use: This code handles movement for the enemies
 Notes: Enemy moves back and forth at a random speed to a target point and back. (Cycle repeats)
 
 */
 #endregion
 
 using UnityEngine;
 using System;
 using System.Collections;
 
 public class EnemyMovement : Enemy {
 
     #region Variables
     //Movement Target
     public Transform farEnd;
 
     //Locations
     private Vector3 startLoc;
     private Vector3 targetLoc;
     private Vector3 currentLoc;
 
     //Time to complete one length
     System.Random rnd = new System.Random();
     public float secondsToComplete;
     #endregion
 
     #region Start
     // Use this for initialization
     void Start ()
     {
         //Movement
         startLoc = transform.position;
         targetLoc = farEnd.position;
 
         //Random
         secondsToComplete = rnd.Next(5, 15); //Sets random to be between 5 & 15 inclusive
     }
     #endregion
 
     #region Update
     // Update is called once per frame
     void Update ()
     {
         //Move if player is not seen
         if (!playerSeen)
         {
             StartCoroutine("Movement");
         }
         
         if (playerSeen)
         {
             StopCoroutine("Movement");
             transform.position = currentLoc;
         }
     }
     #endregion
 
 
     IEnumerator Movement()
     {
         //Moves enemy model between starting location (currentLoc) and a point (targetLoc). 
         //Model will continually move back and forth (as of right now)
         transform.position =
                 Vector3.Lerp(startLoc, targetLoc,
                 Mathf.SmoothStep(0f, 1f,
                 Mathf.PingPong(Time.time / secondsToComplete, 1f)));
 
         currentLoc = transform.position;
 
         yield return null;
     }
 
     //END OF FILE BELOW
 }