google-api-dotnet-client: Unable to connect to Google Sheets using Quickstart tutorial

Hi, I have been running the .NET Quickstart tutorial for the Google Sheets API succesfully for a couple of weeks as Desktop Application. But the last two days it doesn’t seem to connect anymore via OAuth2.

I get an AggregateException on GoogleWebAuthorizationBroker.AuthorizeAsync(…) with the following inner exception.

Any ideas on how to solve this. Thanks!

Google.Apis.Auth.OAuth2.LocalServerCodeReceiver+LimitedLocalhostHttpServer+ServerException:
Unexpected end of network stream reading request line.

   at Google.Apis.Auth.OAuth2.LocalServerCodeReceiver.LimitedLocalhostHttpServer.ReadRequestLine(Func`1 getChar) in C:\Apiary\2020-07-01.13-31-04\Src\Support\Google.Apis.Auth\OAuth2\LocalServerCodeReceiver.cs:line 282
   at Google.Apis.Auth.OAuth2.LocalServerCodeReceiver.LimitedLocalhostHttpServer.GetQueryParamsFromClientAsync(TcpClient client, CancellationToken cancellationToken) in C:\Apiary\2020-07-01.13-31-04\Src\Support\Google.Apis.Auth\OAuth2\LocalServerCodeReceiver.cs:line 266
   at Google.Apis.Auth.OAuth2.LocalServerCodeReceiver.LimitedLocalhostHttpServer.GetQueryParamsAsync(CancellationToken cancellationToken) in C:\Apiary\2020-07-01.13-31-04\Src\Support\Google.Apis.Auth\OAuth2\LocalServerCodeReceiver.cs:line 207
   at Google.Apis.Auth.OAuth2.LocalServerCodeReceiver.GetResponseFromListener(LimitedLocalhostHttpServer server, CancellationToken ct) in C:\Apiary\2020-07-01.13-31-04\Src\Support\Google.Apis.Auth\OAuth2\LocalServerCodeReceiver.cs:line 461
   at Google.Apis.Auth.OAuth2.LocalServerCodeReceiver.ReceiveCodeAsync(AuthorizationCodeRequestUrl url, CancellationToken taskCancellationToken) in C:\Apiary\2020-07-01.13-31-04\Src\Support\Google.Apis.Auth\OAuth2\LocalServerCodeReceiver.cs:line 432
   at Google.Apis.Auth.OAuth2.AuthorizationCodeInstalledApp.AuthorizeAsync(String userId, CancellationToken taskCancellationToken) in C:\Apiary\2020-07-01.13-31-04\Src\Support\Google.Apis.Auth\OAuth2\AuthorizationCodeInstalledApp.cs:line 78
   at Google.Apis.Auth.OAuth2.GoogleWebAuthorizationBroker.AuthorizeAsync(Initializer initializer, IEnumerable`1 scopes, String user, CancellationToken taskCancellationToken, IDataStore dataStore, ICodeReceiver codeReceiver) in C:\Apiary\2020-07-01.13-31-04\Src\Support\Google.Apis.Auth\OAuth2\GoogleWebAuthorizationBroker.cs:line 154
   at Google.Apis.Auth.OAuth2.GoogleWebAuthorizationBroker.AuthorizeAsync(ClientSecrets clientSecrets, IEnumerable`1 scopes, String user, CancellationToken taskCancellationToken, IDataStore dataStore, ICodeReceiver codeReceiver) in C:\Apiary\2020-07-01.13-31-04\Src\Support\Google.Apis.Auth\OAuth2\GoogleWebAuthorizationBroker.cs:line 70