On my system, there is some unpredictable delay between hitting Undo and seeing the created or deleted Node appear/disappear. Sometimes the deleted Node doesn’t actually reappear until I click off-window or drag another node or something. If it bothers you too, it is possible to force a GUI repaint with the following code in ProcessEvents():
if (Event.current.commandName == "UndoRedoPerformed")
{
GUI.changed = true;
}
There’s also an event you can subscribe to if you prefer this approach:
Undo.undoRedoPerformed += MyForceGUIChangedCallback;