Very strange error

Hi all togehter,
as asked in this thread:

https://forums.xamarin.com/discussion/142159/strange-error-2#latest

I have a very strange error.
As before, running as UWP works perfectly, the problem is only in Android.

After updating all files with NuGet and Visual Studio 15.9.5 i get the following error.

try
{
await Table.PullAsync($"all{Identifier}", Table.CreateQuery()).ConfigureAwait(false);
}

        catch (MobileServicePushFailedException push_ex)
        {
            ShowPushError(this.ToString() + " -> PullLatestAsync", push_ex);
        }

        catch (Exception ex)
        {
            Debug.WriteLine("<PullLatestAsync()>Unable to pull items, that is alright as we have offline capabilities: " + ex);
            return false;
        }      
        return true;

The error raises in await Table...…..
and was catched in catch (Excepiion e)

{System.Net.Http.HttpRequestException} System.Net.Http.HttpRequestException
base {System.InvalidOperationException} System.InvalidOperationException
System.Net.WebExceptionStatus.NameResolutionFailure System.Net.WebExceptionStatus

Help is needed very urgend because i have no idea where to look and what to do...

Thanks in Advance
Peter