Using Vuforia, ITrackableEventHandler only triggers on 1 image, not any image.

I am having issues with multi-image tracking and implementing the ITrackableBehaviour.

Here is the expected story: As a user, I want to view a sprite on my camera (think of it as like a crosshairs target) and when I scan any image target, this sprite will fade away on any image recognition and have the sprite fade back in when the image is gone.

I've applied the following script to the target (essentially a sprite image).

The issue is, the fade out of the sprite only occurs when scanning one particular scanned images, versus on 'any' of the scanned images.

 using UnityEngine;
 using System.Collections;
 using Vuforia;
 
 public class Circles: MonoBehaviour, ITrackableEventHandler
 {

     private float startTime; 
     public GameObject circleOne;
     private TrackableBehaviour mTrackableBehaviour;
 
     void Start() {
         isFadeIn = false;
         isFadeOut = false;
         mTrackableBehaviour = GetComponent<TrackableBehaviour>();
         if (mTrackableBehaviour) mTrackableBehaviour.RegisterTrackableEventHandler(this);
     }
 
     public void OnTrackableStateChanged(
         TrackableBehaviour.Status previousStatus,
         TrackableBehaviour.Status newStatus)
     {
         if (newStatus == TrackableBehaviour.Status.DETECTED ||
             newStatus == TrackableBehaviour.Status.TRACKED ||
             newStatus == TrackableBehaviour.Status.EXTENDED_TRACKED)
         {
             // Fade out circles when found
             this.fadeOut();
         }
         else
         {
             // Fade in circles when lost
             this.fadeIn();
         }
     }
 
     public void Update() {
         if (isFadeOut) {
                 ...
         } else if (isFadeIn) {
             ...
         }
     }
 
     private void fadeOut(){
         startTime = Time.time;
         isFadeOut = true;
         isFadeIn = false;
     }
 
     private void fadeIn(){
         startTime = Time.time;
         isFadeIn = true;
         isFadeOut = false;
     }
 }