SocketAsyncResult.CheckIfThrowDelayedException () exception on Android

I have below exception when i want to connect to my api. This exception is happening in some special cases. for example, when I am in my gym, i am able to reproduce it. my gym is having a wireless connection using this service https://www.freefii.de/
when I connect to it, general internet connection is fine and fast but somehow my app is returning this exception every time i make api request.
Any idea what could be the problem?

"type": "System.Net.WebException",
"message": "Error: ConnectFailure (Network subsystem is down)",
"stackTrace": " at System.Net.WebConnection.Connect (System.Net.WebOperation operation, System.Threading.CancellationToken cancellationToken) [0x00217] in :0 \n at System.Net.WebConnection.InitConnection (System.Net.WebOperation operation, System.Threading.CancellationToken cancellationToken) [0x000cc] in :0 \n at System.Net.WebOperation.Run () [0x0009a] in :0 \n at System.Net.WebCompletionSource1[T].WaitForCompletion () [0x00094] in <a13a876c512b4bd799407c195d4b8176>:0 \n at System.Net.HttpWebRequest.RunWithTimeoutWorker[T] (System.Threading.Tasks.Task1[TResult] workerTask, System.Int32 timeout, System.Action abort, System.Func`1[TResult] aborted, System.Threading.CancellationTokenSource cts) [0x000f8] in :0 \n at System.Net.Http.HttpClientHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x002e7] in :0 ",

here is the code I am using;

 private static HttpClient getClient()
        {
                  HttpClientHandler handler = new HttpClientHandler
                    {
                        Proxy = Xamarin.Forms.DependencyService.Get<Helpers.IProxyInfoProvider>().GetProxySettings()
                    };
                     HttpClient _client= new HttpClient(handler);

                  return _client;
     }

 using (HttpClient client = getClient())
       {
                 HttpResponseMessage response = await client.GetAsync(uri, ct)
        }

In Android Project

 public class ProxyInfoProvider : IProxyInfoProvider
    {
        public WebProxy GetProxySettings()
        {
            string proxyHost = JavaSystem.GetProperty("http.proxyHost");
            string proxyPort = JavaSystem.GetProperty("http.proxyPort");

            return !string.IsNullOrEmpty(proxyHost) && !string.IsNullOrEmpty(proxyPort)
                ? new WebProxy($"{proxyHost}:{proxyPort}")
                : null;
        }
    }