Unauthorized Http Response - azure

Question

I am using an Azure Authentication in my Xamarin.Form project, the token received is used for making API calls for authentication purpose.
After some time after the keeping the app in background, again I try to make the API calls it returns "unauthorised".
The token expiration time is set to 30 min. But unauthorised error is not consistent some time it happens as soon as keep the app in background and some time it works fine.
Has anyone faced the same issue.
public async Task<Response> AuthenticatedGet(string uri, string accessToken, string content = null)
{
Uri restUri = new Uri(uri, UriKind.RelativeOrAbsolute);
HttpClient client = new HttpClient();
client.Timeout = TimeSpan.FromSeconds(60);
HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, restUri.ToString());
request.Headers.Add("Accept", "application/json");
request.Headers.Add("Authorization",
string.Format("Bearer {0}", accessToken));
var result = await client.SendAsync(request);
//HttpClient client = new HttpClient();
//client.Timeout = TimeSpan.FromSeconds(60);
//var result = await client.SendAsync(request);
Response sr = new Response();
if (result.IsSuccessStatusCode)
{
string responseString = await result.Content.ReadAsStringAsync();
if (!string.IsNullOrEmpty(responseString))
{
sr.ResponseData = responseString;
sr.IsSuccess = true;
sr.StatusCode = (int)result.StatusCode;
}
}
else if (result.StatusCode == HttpStatusCode.NotFound)
{
sr.ResponseData = $"Service not found at the specifed uri {uri}";
sr.IsSuccess = false;
sr.StatusCode = (int)result.StatusCode;
}
else
{
//var responseString = await result.Content.ReadAsStringAsync();
//JObject jObject = JObject.Parse(responseString);
//var messageProperty = jObject.Property("Message");
//if (messageProperty != null && result.StatusCode == HttpStatusCode.Unauthorized)
//{
// var message = messageProperty.Value?.ToString();
// sr.Message = !string.IsNullOrEmpty(message) ? message : result.ReasonPhrase;
// LogoutUnauthorisedUser?.Invoke(message);
// throw new UnauthorizedAccessException(message);
//}
//sr.Message = result.ReasonPhrase;
//sr.IsSuccess = false;
//sr.StatusCode = (int)result.StatusCode;
//TODO: Handle Unauthorized user
}
return sr;
}
public async Task<ObservableCollection<NIODetails>> GetABCServiceAsync()
{
var uri = string.Format(_hostConfiguration.ABCHostName + _hostConfiguration.ABC, Configuration.ABC);
var resonse = await _httpService.AuthenticatedGet(uri, Constant.ADToken, null);
if (resonse.IsSuccess)
{
var list = JsonConvert.DeserializeObject<ObservableCollection<ABCDetails>>(resonse.ResponseData);
return list;
}
else
{
return null;
}
}