Razor page hubConnection doesn't get async message

This is form in razor page:

<div>
    <b>Message :</b> <input value="@Context" @onchange="@(e => { Context = e.Value.ToString(); })" />
    <button class="btn btn-default" @onclick="@(() => HubConnection.SendAsync("Message", TableId, @playerName, @Context))">Send</button>
</div>

this is my MultiplayerHub function:

 public async Task Message(string tableId, string playername, string context)
        {
            await Clients.GroupExcept(tableId, Context.ConnectionId).SendAsync("NewMessage", playername, context);
        }

and Im receiving "NewMessage" in razor page this way:

protected override void OnInitialized()
{
        HubConnection.On<string, string>("NewMessage", (playername, context) => {
            messages.Add(new Message(playername, context));
        });
}

Problem is that I can't receive signal from hub and add item to list. Form works and it correctly sends variables and message to MultiplayerHub, but then nothing more happens. Does someone know how can I fix it? I have another functions similar to this and it works correct. Github project: https://github.com/dawid628/CheckersApp
Edit: When I use Clients.All.SendAsync(...) it works, but to all hubs.