High load ASP.NET application running as Windows Service not stopping

Question

An asp.net application (running on Kestrel) running as a Windows Service has trouble stopping during high load.

The setup:

[...]

    var config = WebHostBuilderHelper.GetConfig();

            var hostBuilder = new WebHostBuilder().UseKestrel(options => options.ConfigureEndpoints())
                                                  .UseConfiguration(config)
                                                  .UseStartup<Startup>()
                                                  .UseSerilog((hostingContext, loggerConfiguration) => loggerConfiguration.ReadFrom.Configuration(hostingContext.Configuration))
                                                  .UseContentRoot(AppDomain.CurrentDomain.BaseDirectory);

            if (Debugger.IsAttached || args.ToList()
                                           .Contains("console"))
            {
                var host = hostBuilder.Build();

                host.Run();
            }
            else
            {
                var host = hostBuilder.UseContentRoot(pathToContentRoot)
                                      .Build();

                host.RunAsCustomService();
            }

RunAsCustomService:

    public static class WebHostServiceExtensions
    {
        public static void RunAsCustomService(this IWebHost host)
        {
            var webHostService = new CustomWebHostService(host);
            ServiceBase.Run(webHostService);
        }
    }

internal class CustomWebHostService : WebHostService
    {
        private ILogger _logger;

        public CustomWebHostService(IWebHost host) : base(host)
        {
            Console.Write("CustomWebHostService start");
            _logger = host.Services
                          .GetRequiredService<ILogger<CustomWebHostService>>();
        }
[...]
    }

When stopping the service, it correctly receives the Stop-signal from Windows (can be verified by both logs and attaching debugger) -- and it correctly stops very quickly when not under load. During OnStop(); StopAsync() is called on the host, and then, eventually, it is disposed. I'm guessing the StopAsync does not stop very well when there are a large amount of requests being made to at the same time. Some signal being lost perhaps? During normal operation all objects are correctly cleaned up or otherwise disposed.

Best regards,