OnTrigger ignoring all collisions but the first

Hi everybody:

I have a huge problem. I'm trying to implementing a waypoint AI system for my racing game. I have all the waypoints in my circuit stored in a list, and in the OnTriggerEnter(), when it arrives to the first waypoint, the target of my AI car point to the next waypoint. Also, when OnTriggerExit() is active, it add 1 to the variable that control the target to be pointed. But it doesn't works furthermore, only with the first collision. Here are my codes:

 private Transform targetObject;
 private int i = 0; // This variable will control the current waypoint to follow
 public List<Transform> waypoints;
 
 private KartController kart;

 void Start () 
 {
     // keep a reference to the kart component
     kart = GetComponent<KartController>();
     targetObject = waypoints [i];
 }
 

     void OnTriggerEnter(Collider other)
 {
     if (other.tag == "Waypoint") {
         targetObject = waypoints [i+1];
     }
 }

 void OnTriggerExit(Collider other)
 {
     if (other.tag == "Waypoint") {
         i++;
         return;
     }
 }

}

Can you help me? Thanks a lot!