Crash in mono on HttpClient().PostAsync

I need to post data to a webservice from my xamarin.forms application. I get a mono crash on my ipod touch when client.PostAsync is called. I don't (know how to?) get any usable crash data. One thing I notice is that even though it is an awaited async call, it does not appear to wait for a response (the response object is null) before moving on. It then crashes in the next couple of seconds. It looks like it might be that it crashes when it gets a response and tries to resume the thread.

It never hits any breakpoints, it just hard stops. I have included an example call, the post data doesn't seem to make a difference. I get the same response when I post an empty stringcontent.

I don't get the same crash in the emulator, only when it is deployed to a device. Right now and for the foreseeable future this app will only be used on an ipod, so I am happy to move the post from xamarin.forms and into the ios code if that would be preferable/more stable.

public static async Task<bool> UpdateContact(App app, string oldContactName)
        {
            try
            {
                var c = new
                {
                    Name = app.Settings.SiteContactName,
                    Email = app.Settings.SiteContactEmail,
                    CellNumber = app.Settings.SiteContactCellPhone,

                    siteCode = app.Settings.SiteName,
                    oldContactName = oldContactName
                };
                await DoPost(app, "UpdateContact", c);
                return true;
            }
            catch (Exception exc)
            {
                await AddLog(app, "Network Error", string.Format("There was an error updating the contact at {0}.  MSG: {1}", DateTime.Now.ToString("yyyy/MM/dd HH:mm"), exc.Message));
                return false;
            }
        }

        private static async Task DoPost(App app, string action, object data)
        {
            await DoPost(app.Settings.WebServiceUrl, action, data, app.BatteryLevel);
        }
private static async Task DoPost(string baseUrl, string action, object data, int batteryLevel = -1)
        {
            var url = baseUrl + action;

            var postContent = GetHttpContentFromObject(data, batteryLevel);
            HttpResponseMessage response;
            using (var client = new HttpClient())
            {
                response = await client.PostAsync(url, postContent);
            }

            if (response.IsSuccessStatusCode == false)
            {
                throw new Exception(string.Format("Could not reach web service. Code:{0} MSG:{1}", response.StatusCode, response.Content.ToString()));
            }
            var contentVal = await response.Content.ReadAsStringAsync();

            if (contentVal != "")
            {
                throw new Exception(string.Format("Got an error from the web service.  MSG:" + contentVal));
            }


        }

        private static HttpContent GetHttpContentFromObject(object data, int batteryLevel = -1)
        {
            var kvp = new List<KeyValuePair<string, string>>();
            if (data != null)
            {
                var props = data.GetType().GetRuntimeProperties();
                if (props != null)
                {
                    foreach (var p in props)
                    {
                        try
                        {
                            var val = p.GetValue(data);
                            kvp.Add(new KeyValuePair<string, string>(p.Name, (val != null ? val.ToString() : "")));
                        }
                        catch(Exception exc)
                        {
                            var e = exc;
                        }
                    }
                }
                kvp.Add(new KeyValuePair<string, string>("batteryLevel", batteryLevel.ToString()));
            }
            return new FormUrlEncodedContent(kvp);
        }