A replacement base class to use instead of Editor. Inheriting from this editor class will allow you to validate properties without encountering the OnValidate garbage collection bug. OnValidateProperty is also guaranteed to only execute when a change is made in the Inspector Window. It doesn't run when loading an asset into memory or loading a s…

BaseMonoBehaviourEditor.cs

[CanEditMultipleObjects, CustomEditor(typeof(BaseMonoBehaviour), true)]
public class BaseMonoBehaviourEditor : Editor
{
    public override void OnInspectorGUI()
    {
        serializedObject.Update();
 
        SerializedProperty iterator = serializedObject.GetIterator();
        bool enterChildren = true;
        while (iterator.NextVisible(enterChildren))
        {
            enterChildren = false;
 
            OnPropertyGUI(property);
        }

        serializedObject.ApplyModifiedProperties();
    }
 
    public void OnPropertyGUI(SerializedProperty property)
    {
        OnPropertyGUI(property, new GUIContent(property.displayName, property.tooltip));
    }

    public void OnPropertyGUI(SerializedProperty property, GUIContent label)
    {
        BaseMonoBehaviour t = target as BaseMonoBehaviour;
 
        EditorGUI.BeginChangeCheck();

        DrawProperty(property, label);
 
        if (EditorGUI.EndChangeCheck())
        {
            property.serializedObject.ApplyModifiedProperties();
            property.serializedObject.Update();
            t.OnValidateProperty(property.name);
        }
    }

    public void OnPropertyGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        BaseMonoBehaviour t = target as BaseMonoBehaviour;
 
        EditorGUI.BeginChangeCheck();

        DrawProperty(position, property, label);
 
        if (EditorGUI.EndChangeCheck())
        {
            property.serializedObject.ApplyModifiedProperties();
            property.serializedObject.Update();
            t.OnValidateProperty(property.name);
        }
    }
    
    public virtual Rect GetPropertyControlRect(SerializedProperty property, GUIContent label, params GUILayoutOption[] options)
    {
        return EditorGUILayout.GetControlRect(!string.IsNullOrEmpty(label.text), EditorGUI.GetPropertyHeight(property, label, true), options);
    }

    protected virtual void DrawProperty(SerializedProperty property, GUIContent label, params GUILayoutOption[] options)
    {
        Rect position = GetPropertyControlRect(property, label, options);
        DrawProperty(position, property, label);
    }
 
    protected virtual void DrawProperty(Rect position, SerializedProperty property, GUIContent label)
    {
        EditorGUI.PropertyField(position, property, label);
    }
}