Serializable class doesn't store list<>

Hi everyone, I have a problem, that I can't store the list "distances" inside my serializable class. The UnityEditor "forgets" it after a cycle. The class RAYpoint on the other hand is stored ,therefore I can get x,y,z. Guess its a problem with list in general. I tried some solutions offered by other users, sadly so far, I didn't get it to work. Hope someone can point me in the right direction. Cheers

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 [System.Serializable]
 public class RAYpoint{
 
     public RAYpoint(Vector3 vec) { vector = vec; }
     public Vector3 vector;
     public bool updated = false;
 
     [SerializeField]
     public List<_DistancePoint> distances = new List<_DistancePoint>();
     public RAYpoint[] neighbors = new RAYpoint[0];
 
     public void reset(){
         distances = new List<_DistancePoint>();
         neighbors = new RAYpoint[0];
     }
     
     public RAYpoint[] GetNeighbors(){
 
         if (!updated) {
 
             SortDistance ();
 
             neighbors = new RAYpoint[distances.Count];
 
             for(int i = 0; i < distances.Count; i++){
                 neighbors[i] = distances[i].point;
             }
         }
         
         return neighbors;
     }
 
     public void AddDistance(float distance, RAYpoint point){
         updated = false;
         
         if (distances == null) {
             distances = new List<_DistancePoint>();
         }
         
         distances.Add (new _DistancePoint (distance, point));
     }
 
     
     public void SortDistance(){
         if (!updated) {
             distances.Sort(
                 delegate(_DistancePoint p1, _DistancePoint p2) {
                 return p1.distance.CompareTo (p2.distance);
             });
         }
         updated = true;
     }
 
     public float x {
         get {
             return vector.x;
         }
         set
         {
             vector = new Vector3(value, vector.y, vector.z);
         }
     }
     
     public float y {
         get {
             return vector.y;
         }
         set
         {
             vector = new Vector3(vector.x, value , vector.z);
         }
     }
     
     public float z {
         get {
             return vector.z;
         }
         set
         {
             vector = new Vector3(vector.x, vector.y, value);
         }
     }
 
     
     public static implicit operator Vector3(RAYpoint obj){
         return obj.vector;
     }
     //  User-defined conversion from double to Digit
     public static implicit operator RAYpoint(Vector3 vector){
         return new RAYpoint(vector);
     }
     
     public override string ToString(){
         return vector.ToString();
     }
 
     /**************************************/
     [System.Serializable]
     public class _DistancePoint{
         
         public float distance { get; set; }
         public RAYpoint point { get; set; }
         
         public _DistancePoint(float distance, RAYpoint point){
             
             this.distance = distance;
             this.point = point;
         }
         
         public override string ToString(){
             return "Distance: " + distance + "   Point: " + point;
         }
     }
 
 }