Xamarin Forms Android error System.Net.WebExceptionStatus.TrustFailure

Question

I am having a challenge with my Xamarin Forms Android app in Visual Studio 2015 Enterprise edition.

Below is my helper class which makes all calls to my WebAPIs

    public string CallWebService(string ps_URI)
    {
        HttpClient lobj_HTTPClient = null;
        HttpResponseMessage lobj_HTTPResponse = null;
        string ls_Response = "";
        string ls_Prefix = "";
        //We assume the internet is available. 
        try
        {
            ls_Prefix = Device.OnPlatform<string> (App.APISecurePrefix, App.APIPrefix, App.APIPrefix);
            //Get the Days of the Week
            //lobj_HTTPClient = new HttpClient(new NativeMessageHandler());
            lobj_HTTPClient = new HttpClient();
            lobj_HTTPClient.BaseAddress = new Uri(App.APISecurePrefix);
            lobj_HTTPClient.DefaultRequestHeaders.Accept.Clear();
            lobj_HTTPClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

            var lobj_Result = lobj_HTTPClient.GetAsync(ps_URI);

            while (!lobj_Result.IsCompleted)
            {
                Debug.WriteLine("WebAPICaller-CallWebService-1: URI:" + ps_URI);
                Task.Delay(100);
            }
            //GEt the http response object
            lobj_HTTPResponse = lobj_Result.Result;

            if (!lobj_HTTPResponse.IsSuccessStatusCode)
            {
                App.ProcessException(new Exception(lobj_HTTPResponse.ReasonPhrase));
            }
            else
            {
                var lobj_DataResult = lobj_HTTPResponse.Content.ReadAsStringAsync();

                while (!lobj_DataResult.IsCompleted)
                {
                    Debug.WriteLine("WebAPICaller-CallWebService-2");
                    Task.Delay(100);
                }
                ls_Response = lobj_DataResult.Result;
            }
        }
        catch (Exception ex)
        {
            App.ProcessException(ex);
        }
        finally
        {
            if (lobj_HTTPClient != null)
                lobj_HTTPClient.Dispose();
            if (lobj_HTTPResponse != null)
            {
                lobj_HTTPResponse.Dispose();
            }
            Debug.WriteLine("WebAPICaller-CallWebService-1: Done");
        }

        return ls_Response;

    }

It works fine on Windows phones but when I attempt to make WebAPI calls on the Android Emulator an exception is thrown as follows (See the TrustFailure):

Please note I am calling the WebAPI over a secure connection (https) and the server I am contacting does support both HTTP and HTTPS access to the WebAPIs.

I am using the latest stable version of Xamarin forms (2.3.3.180). I have removed the use of ModernHTTPClient. I did try to use the latest beta version of Xamarin Forms but then my needed components would not install so I went back to the last stable version.

Any idea how I can resolve this? If the solution involves doing anything with the Java or Android components outside of Visual Studio 2015, please provide specific details as I am not that familiar with how to do many Android / Java related things.