The error happens when calling if (_context.SessionToken != null) return; there is no loop.
ThomsonReuters.Dss.Api.TooManyRequestsException: Too many requests for throttling category "Authentication", user id "". Approximately 408 requests were made in 300 seconds. at ThomsonReuters.Dss.Api.Core.HttpOData.Http.HttpClientExceptionDecorator.ParseResponseError(Uri uri, HttpResponseMessage response) at ThomsonReuters.Dss.Api.Core.HttpOData.Http.HttpClientExceptionDecorator.HandleExceptions(Func`1 method, Uri uri, String methodName, Boolean isIdempotent) at ThomsonReuters.Dss.Api.Core.HttpOData.Http.HttpClientExceptionDecorator.HandleExceptions(Func`1 method, Uri uri, String methodName, Boolean isIdempotent) at ThomsonReuters.Dss.Api.Core.HttpOData.Http.HttpAsyncJobStrategy.InvokeAsync(Func`2 method, Boolean pollReturnAfterHeaders, CancellationToken cancellationToken, IProgress`1 progress) at ThomsonReuters.Dss.Api.Core.HttpOData.HttpODataClient.InternalExecuteAsync(IHttpClient httpClient, Type resultEntityType, Uri uri, String httpMethod, OperationParameter[] parameters, String queryOptions, Nullable`1 waitOverride, CancellationToken cancellationToken, IProgress`1 progress) at ThomsonReuters.Dss.Api.Core.HttpOData.HttpODataClient.ExecuteAsync[T](Uri uri, String httpMethod, Boolean isSingle, OperationParameter[] parameters, String queryOptions, CancellationToken cancellationToken, IProgress`1 progress) at ThomsonReuters.Dss.Api.Core.OperationsBaseForHttpODataClient.CallOnHttpODataClient[T](DssDataServiceContext context, Func`2 method, Boolean allowAutomaticDecompression) at ThomsonReuters.Dss.Api.Core.Helper.ReAuthenticateIfNecessaryAsync[T](IDssDataServiceContext context, Func`1 method, CancellationToken cancellationToken) at ThomsonReuters.Dss.Api.Core.OperationsBaseForHttpODataClient.ExecuteAsync[T](DssDataServiceContext context, Uri uri, String httpMethod, Boolean isSingle, OperationParameter[] parameters, String queryOptions, CancellationToken cancellationToken, IProgress`1 progress) at ThomsonReuters.Dss.Core.RestApi.Threading.Tasks.AsyncHelper.RunSync[TResult](Func`1 func) at ThomsonReuters.Dss.Api.Core.OperationsBase.InvokeSynchronously[T](Func`1 action) at ThomsonReuters.Dss.Api.Core.OperationsBase.Execute[T](DssDataServiceContext context, Uri uri, String httpMethod, Boolean isSingle, OperationParameter[] parameters, String queryOptions) at ThomsonReuters.Dss.Api.DssDataServiceContext.<>c__DisplayClass12`1.<Execute>b__11() at ThomsonReuters.Dss.Api.Core.Helper.ReAuthenticateIfNecessary[T](IDssDataServiceContext context, Func`1 method) at ThomsonReuters.Dss.Api.DssDataServiceContext.Execute[TElement](Uri requestUri, String httpMethod, Boolean singleResult, OperationParameter[] operationParameters, String queryOptions) at ThomsonReuters.Dss.Api.Authentication.AuthenticationContext.RequestToken(Credentials credentials) at ThomsonReuters.Dss.Api.DssDataServiceContext.Authenticate(Uri serviceRoot, NetworkCredential networkCredential) at ThomsonReuters.Dss.Api.DssDataServiceContext.get_SessionToken() at