Entity Framework Core 2.0: Error when enumerating over query with group

I have the following method which simply iterates over orders grouped by client ID.

static void LinqWithInto()
{

    using (var db = new EFContext())
    {
        var orders = db.Orders.Include(o => o.Client);
        orders.Load();

        var query = from order in orders
                    group order by order.ClientId into g
                    select new { ClientId = g.Key, Count = g.Count(), Orders = g };

        foreach (var group in query)
        {
            WriteLine($"Client Id: {group.ClientId}, Number of orders: {group.Count}");
            foreach (var order in group.Orders)
                WriteLine($"\tOrder Id: {order.OrderId}, Client Id: {order.Client.ClientId}, Client Name: " +
                    $"{order.Client.Name} Payment: {order.Payment}");
        }

    }
}

The query fetches orders with associated clients:

[Table("Order")]
public class Order
{
    public int OrderId { get; set; }
    public int ClientId { get; set; }
    public double Payment { get; set; }

    [ForeignKey("ClientId")]
    public Client Client { get; set; }
}

[Table("Client")]
public class Client
{
    public int ClientId { get; set; }
    public string Name { get; set; }
    public string Address { get; set; }

    public List<Order> Orders { get; set; }
}

The code works well in EF6, but in EF Core I get the following error (the variable query in foreach loop is highlighted):

System.ArgumentException: 'Expression of type 'System.Object' cannot be used for parameter of type 'Microsoft.EntityFrameworkCore.Metadata.IEntityType' of method 'Void StartTracking(System.Object, Microsoft.EntityFrameworkCore.Metadata.IEntityType)''

I wonder what's wrong here?