this.Clients are disposed SignalR

Question

At the time of the user's connection, everything is going well. When I have a product update (it becomes available for sale), the OnProductStartSales event is called. But there is one problem, the message does not come to the client because the list of clients in the hub is disposed. Here is the code of my hub.

public class SalesHub : Hub
{
    private readonly ProductDatabaseListener _listener;

    public SalesHub(ProductDatabaseListener listener)
    {
        _listener = listener ?? throw new ArgumentNullException(nameof(listener));
        _listener.OnProductStartSales += (s, p) => ProductStartSales(p);
        _listener.OnProductDataChanged += (s, p) => ProductDataChanged(p);
    }

    public async Task ListenProduct(string productId)
    {
        await this.Groups.AddToGroupAsync(Context.ConnectionId, productId);
    }

    private async Task ProductStartSales(Product product)
    {
        await this.Clients.Group(product.Id).SendAsync("StartSales", product.Id);
        // await this.Clients.All.SendAsync("StartSales", product.Id);
    }

    private async Task ProductDataChanged(Product product)
    {
        await this.Clients.Group(product.Id).SendAsync("DataChanged", product);
    }
}

Here is the code of listener.

public class ProductDatabaseListener
{
    private readonly IRepository<Product> _repository;
    private readonly object _locker = new object();

    public ProductDatabaseListener(IServiceProvider serviceProvider)
    {
        using (var scope = serviceProvider.CreateScope())
        {
            _repository = scope.ServiceProvider.GetRequiredService<IRepository<Product>>() ?? throw new ArgumentNullException(nameof(_repository));
        }
    }

    public event EventHandler<Product> OnProductStartSales;
    public event EventHandler<Product> OnProductDataChanged;

    // Need better performance...
    public async Task ListenMongo()
    {
        while (true)
        {
            var products = await _repository.GetRange(0, int.MaxValue);
            var date = DateTime.Now;
            List<Task> tasks = new List<Task>();

            foreach (var product in products)
            {
                if (product.IsSalesStart)
                {
                    continue;
                }

                if (product.StartOfSales <= date)
                {
                    product.IsSalesStart = true;
                    OnProductStartSales?.Invoke(this, product);
                    tasks.Add(_repository.Update(product));
                }
            }

            Task.WaitAll(tasks.ToArray());

            await Task.Delay(1000);
        }
    }
}

Here is the client code

"use strict";

var connection = new signalR.HubConnectionBuilder().withUrl("/salesHub").build();

connection.on("ReceiveMessage", function (id) {
    var li = document.createElement("li")
    document.getElementById("fromHub").appendChild(li)
    li.textContent = id;
});

connection.on("startSales", function (id) {
    var productId = document.getElementById("objectId").getAttribute("value");
    if (productId == id) {
        var button = document.getElementById("buy")
        button.hidden = false
    }
});

connection.logging = true;

connection.start().then(function () {
    var productId = document.getElementById("objectId").getAttribute("value");
    connection.invoke("ListenProduct", productId).catch(function (err) {
        return console.error(err.toString());
    });
    event.preventDefault();
}).catch(function (err) {
    return console.error(err.toString());
});