"The service implementation object was not initialized or is not available" when calling a custom wcf service application in SP2013

I have a simple Custom Service Application that hosts a WCF service. the service has a simple method

    [ServiceContract]
    [XmlSerializerFormat]
    public interface IWCFServiceContract
    {
        [OperationContract]
        Client GetClient(int clientId);

        [OperationContract]
        DateTime GetCurrentDateTime();
    }

service app methods look like this:

        public Client GetClient(int clientId)
        {
            try
            {
                MonitoringDBDataContext ctx = new MonitoringDBDataContext(Database.DatabaseConnectionString);

                return (from c in ctx.Clients
                        where c.Id == clientId
                        select c).Single();
            }
            catch (Exception ex)
            {
                SPDiagnosticsService.Local.WriteTrace(0, new SPDiagnosticsCategory("xxxx", TraceSeverity.Unexpected, EventSeverity.Error), TraceSeverity.Unexpected, ex.Message, ex.StackTrace);
                throw new FaultException(new FaultReason(ex.Message), new FaultCode(ex.InnerException.Message));
            }
        }

        public DateTime GetCurrentDateTime()
        {
            return DateTime.Now;
        }

From a client console application, I call the GetCurrentTime() method and it fails with "The service implementation object was not initialized or is not available". My client code is:

 ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(delegate { return true; });
                DataContext _dc = new DataContext();


                using (WCFServiceContractClient _ctx = new WCFServiceContractClient())
                {
                    _ctx.ClientCredentials.Windows.ClientCredential = new NetworkCredential("xxxx", "xxxxx", "xxxx");
                    //Client client = _ctx.GetClient(1);
                    DateTime time = _ctx.GetCurrentDateTime();

                                   }

i can do a _ctx.Open() with no issues, but when i call that very simple method, it fails. do note that im calling this over https. my bindings seem correct. but im accessing through a web app that has both http and extended to https. i expect to either use both http and https or just https.