Resources.FindObjectsOfTypeAll(typeof(Material))) not working correctly

I am working on a editor script to detect duplicate materials within a project and show this through a editor script. When I started the script Resources.FindObjectsOfTypeAll(typeof(Material))) would find all the materials within my project, leading to list of several hundreds off materials showing up. After I try'd to order this list through code the Resources.FindObjectsOfTypeAll(typeof(Material))) only seems to find the 18 materials pre- made by unity.

Why is this command suddenly acting different then before ? I tried going back a step and rewrite things, but that did not seem to help either. The basics if been working from was this script. Am I doing something wrong?

 using UnityEngine;
 using UnityEditor;
 using System.Collections.Generic;
 
 public class DetectMaterialNew : EditorWindow
 {
     private Vector2 scrollPos;
     private bool groupEnabled;
 
     List<Material> arrayOfMaterials = new List<Material>();
 
     [MenuItem("Window/Detect Duplicate Material %g")]
     static void Init()
     {
         DetectMaterialNew window = (DetectMaterialNew)EditorWindow.GetWindow(typeof(DetectMaterialNew));
     }
 
     void OnGUI()
     {
         GUILayout.Label("Click to detect Duplicates", EditorStyles.boldLabel);
         if (GUILayout.Button("Detect Material"))
         {
             DetectAllMaterials();
         }
 
         if (groupEnabled)
         {
             scrollPos = EditorGUILayout.BeginScrollView(scrollPos);
             EditorGUILayout.BeginHorizontal();
             EditorGUILayout.BeginVertical();
 
             GUILayout.Label("Total duplicate materials");
             for (int i = 0; i < arrayOfMaterials.Count; i++)
             {
                 EditorGUILayout.LabelField(i.ToString(), arrayOfMaterials[i].name);
             }
 
             EditorGUILayout.EndVertical();
             EditorGUILayout.BeginVertical();
 
             GUILayout.Label("Materials"); 
             for (int i = 0; i < arrayOfMaterials.Count; i++)
             {
                 EditorGUILayout.ObjectField(arrayOfMaterials[i], typeof(Material), true);
             }
 
             EditorGUILayout.EndVertical();
             EditorGUILayout.EndHorizontal();
             EditorGUILayout.EndScrollView();
         }
     }
 
     void DetectAllMaterials()
     {
         foreach (Material c in Resources.FindObjectsOfTypeAll(typeof(Material))) 
         {
             arrayOfMaterials.Add(c);
         }
         groupEnabled = true;
     }
 }