How do I get enemies to only chase me in certain areas

I'm am currently using a script that works fine at one moment and then the next moment certain enemies don't work while others do - I am confused

 void Update() 
      {
          if(Antagonist.attackStage <= PlayerStage.playerStage) 
          {
              transform.position = Vector2.MoveTowards(transform.position, target.position, speed * 
                Time.deltaTime);   
              animator.SetFloat("Walking", 3);
          }
          else
          {
              animator.SetFloat("Walking", 1);
          }
      }