Exception when using Firebase streaming

Hi,
When I try to read data from Firebase using FirebaseDatabase.net Library I receive Newtonsoft.Json.JsonReaderException exeptionn

this code works

Imports Firebase.Database
Imports Firebase.Database.Query
Public Class Form1
    Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim client As New FirebaseClient("https://abcd.asia-southeast1.firebasedatabase.app/")
        Dim gesture = Await client _
            .Child("gestures") _
            .Child("last_gesture") _
            .OnceSingleAsync(Of String)()
        If gesture IsNot Nothing Then
            Label1.Text = gesture
        Else
            Label1.Text = "..."
        End If
        Console.WriteLine(gesture)
    End Sub
End Class

but this code does not work when using streaming

Imports Firebase.Database
Imports Firebase.Database.Query
Public Class Form1
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Dim client As New FirebaseClient("https://abcd.asia-southeast1.firebasedatabase.app/")
        client.Child("gestures").Child("last_gesture").AsObservable(Of String)() _
        .Subscribe(Sub(f)
                       Console.WriteLine(f.Object)
                       If f.Object IsNot Nothing Then
                           Label1.Invoke(Sub() Label1.Text = f.Object)
                       End If
                   End Sub)
    End Sub
End Class

How can I solve this issue
Thank you in advance