Help with this script? Keeps moving my objects around in run-time?

The purpose of this script is when attached to a game object it creates a hovering effect. The only issue is that when play button is hit and the game is running the object that have this script move to different locations. They dont seem to stay in the location I've put them in during edit. What could be causing this?

  public class hoveringeffect : MonoBehaviour {
  //public float horizontalSpeed;
   public float verticalSpeed;
   public float amplitude;

 public Vector3 tempPosition;
 void Start () {
     tempPosition = transform.position;
 }
 
 // Update is called once per frame
 void Update () {
     //tempPosition.x += horizontalSpeed;
     tempPosition.y = Mathf.Sin(Time.realtimeSinceStartup * verticalSpeed) * amplitude;
     transform.position = tempPosition;
 }
 }