Changes to custom serializable object not saved to disk

I already asked that question on the forum (link) but I got no answer.

I created my own asset type by deriving from ScriptableObject. Because my class contains data that Unity can't serialize I implemented ISerializationCallbackReceiver as well. I do pretty much the same thing than in the example from the documentation.

It looks like this

     public partial class Graph : ScriptableObject, ISerializationCallbackReceiver
     {
       // Data that Unity can't serialize because INode is an interface
       private List<INode> mNodes;
      
       // Data that Unity can serialize because Connection is a serializable struct
       [SerializeField] [HideInInspector] private List<Connection> mConnections;
      
       // For serialization only
       [SerializeField] [HideInInspector] private List<SpecificNode> mSpecificNodes;
      
      
      
       public void OnBeforeSerialize()
       {
         // Move the nodes from mNodes to mSpecificNodes so they can be serialized
         mSpecificNodes.Clear();
         foreach (INode node in mNodes)
         {
           SpecificNode specificNode = node as SpecificNode;
           if (specificNode != null)
             mSpecificNodes.Add(specificNode);
         }
       }
      
       public void OnAfterDeserialize()
       {
         // Move the nodes back from mSpecificNodes to mNodes
         mNodes.Clear();
         foreach (SpecificNode node in mSpecificNodes)
           mNodes.Add(node);
         mSpecificNodes.Clear();
       }
     }
 

Serialization works perfectly. I made my own editor to edit my assets and within it I use Undo.RecordObject() to record the changes on the undo stack and that works perfectly as well.

What doesn't work is that the changes I make to my asset into the OnBeforeSerialize() method are not saved. In my example above, the content of mConnections is saved, but not the content of mSpecificNodes. That mean if I quit Unity and then open my project again, I get my connections back but no my nodes (mSpecificNodes is empty).

I tried setting my object dirty with EditorUtility.SetDirty() after I modify it but it doesn't change anything. Unity doesn't seem to notice that anything needs to be saved.

What did I miss ?