Flutter Item ExpansionPanelList doesn't change state

Question

I am trying to retrieve data from API, that's works nice.

After that I want to show my data in a ExpansionPanelList, which is builded by a method:

class _CartaPageState extends State<CartaPage> {

  
  @override
  Widget build(BuildContext context) {
    // Nos suscribimos al provider
    final productoService = Provider.of<ProductoService>(context);
    final List<Producto> productos = productoService.productos; 
    _productosItems = productosToItem(productos);
    return Scaffold(
      body: Container(
        height: double.infinity,
        width: double.infinity,
        child: ListView(
          children: [
            ExpansionPanelList(
              animationDuration: Duration(milliseconds: 300),
              expansionCallback: (int index, bool isExpanded) {
                setState(() {
                  _productosItems[index].isExpanded = !isExpanded;
                  //productosItems[index].isExpanded = !productosItems[index].isExpanded;
                });
              },
              //children: productosToItem(productoService.entrantes).map<ExpansionPanel>((Item item) {
              children: _productosItems.map<ExpansionPanel>((Item item) {
                return ExpansionPanel(
                  headerBuilder: (context, isExpanded) {
                    return ListTile(
                      title: Text(item.headerValue),
                    );
                  },
      ................

The data is shown perfect, but the state is not refreshing on my ItemModel, I think the problem is because the widget is redrawing each time I touch the panel list, that retrieve (again) data from the API and never changes the state.

How can I resolve it?

Thank you in advance

EDIT: CartaPage is wraped by:

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (_) => ProductoService()),
      ],
      child: MaterialApp(
        debugShowCheckedModeBanner: false,
        title: 'Material App',
        home: CartaPage()
      ),
    );
  }
}

EDIT 2:

I agree I am losing state, this it the method to convert Product to Item:

List<Item> productosToItem(List<Producto> productos) {
  return List.generate(productos.length, (index) {
    return Item(
      headerValue: productos[index].tipo,
      expandedValue: productos[index].nombre,
    );
  });
}