Casting a GraphView node using GetNodeByGuid() returns null

I'm trying to create a visual scripting tool using GraphView. I want different types of Nodes for the different options (Such as show message, add player EXP and so on). All my nodes inherit from my rpg_EventNode class, which itself inherits from the GraphView Node class.

When I go to save my event, I create a list of rpg_EventNodes.

 private List<rpg_EventNode>  _nodes => _eventGraph.nodes.ToList().Cast<rpg_EventNode>().ToList();

Then, when I've found the node I want to save, I need to cast it into it's specific type.

 foreach (var node in _nodes) 
    {
       switch(node.nodeType)
            {
                case 101 :
                   var messNode = (rpg_MessageEventNode) _eventGraph.GetNodeByGuid(node.GUID);
                            //Save node specific data
                   break;
                          //Annnnddddd so on.....

The problem is, this is returning null. Any ideas why?