Extending unity UI Button problem

I have custom button that extends from UnityEngine.UI.Button, something like this:

 using UnityEngine;
 using UnityEngine.UI;
 using System;
 
 [Serializable]
 public class MyButton : Button {
   public float testFloat;
   public Image testImage;
   public Sprite testSprite;
 }

Then my editor class:

 using UnityEngine;
 using UnityEngine.UI;
 using UnityEditor;
 using UnityEditor.UI;
 
 [CustomEditor(typeof(MyButton))]
 [CanEditMultipleObjects]
 public class MyButtonEditor : ButtonEditor {
   SerializedProperty floatProp;
   SerializedProperty imageProp;
   SerializedProperty spriteProp;
 
   public override void OnInspectorGUI()
   {
     serializedObject.Update();
 
     floatProp = serializedObject.FindProperty("testFloat");
     imageProp = serializedObject.FindProperty("testImage");
     spriteProp = serializedObject.FindProperty("testSprite");
 
     //Normal button options
     base.OnInspectorGUI();
 
     EditorGUILayout.PropertyField(floatProp, new GUIContent("Test Float"));
     EditorGUILayout.PropertyField(imageProp, new GUIContent("Test Image"));
     EditorGUILayout.PropertyField(spriteProp, new GUIContent("Test Sprite"));
 
     serializedObject.ApplyModifiedProperties();
   }
 }

My problem is that this code works on a new/clean project but when I add it to my project I can't drag or set values to the class variables. Even the float variable, that I can change on the editor, when I reload the scene the value isn't saved. So basically they appear on the editor but for Image and Sprite I can't set values and float I can change the value but does nothing...

At first I was setting the values directly like:

 component.testFloat = EditorGUILayout.FloatField("Test Float", component.testFloat);
 component.testImage = (Image)EditorGUILayout.ObjectField("Test Image", component.testImage, typeof(Image), true);
 component.testSprite = (Sprite)EditorGUILayout.ObjectField("Test Sprite", component.testSprite, typeof(Sprite), true);

Then I read that this will not work with prefabs and that is what I want.

The new/clean project is set to the same platform as my project. I spent a lot of time trying to figure why this doesn't work on the project that I want. I don't have any errors on console...

Anyone had a similar problem that can point me to a direction? My project has a considerable size so maybe is something that is creating a conflict but without any console error will be hard to know what.

Thanks!