C# StartBackgroundProcess not runing Async

I have a C# WCF Service hosted in IIS 8.5 which has a simple Client webform consisting of a ComboBox for data entry. The ComboBox can be populated manually or via barcode scanner on the users mobile device. Every time the user uses scanned input the scanned value is written to a database table with UserId, dateTime & value. I have an API which will return the last scanned input for a user based on dateTime scanned.

So I now have a webform which can take its input either manually or via scanned input. If there is no selected value in the comboBox then I want to run a background job to call the API and return any scanned input value to the ComboBox.  

CheckForScannedTransactions below is part of the Client WebForm1 and it calls the background job StartBackgroundProcess passing parameters MyBGJobParms. I expected control to return to UI but when there is no scanned input to return control never returns to the UI despite RunWorkerAsync. Why is this ?

In this scenario every logged on user will call CheckForScannedTransactions() to check for their own scanned input. Is there a better way of doing this ? Could I for instance have just 1 background job running continuously and updating scanned input to each users webform page. Is that possible if so How so?

//CheckforSacnnedTransactions will run in background and populate any scanned value to ComboBox if ComboBox is empty 
if (ComboBox1.SelectedIndex == -1 )
{
    CheckForScannedTransactions ();
}

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public void  CheckForScannedTransactions()
        {
            BGJobParms MyBGJobParms= new BGJobParms();
            MyBGJobParms.BGJobName = "BGJOB01";
            MyBGJobParms.BGJobDescription = "Check for Barcode Scanned Transactions";
            MyBGJobParms.BGJobThreadName = "TiosClientBackgroundWorkerThread";
            MyBGJobParms.BGJobMaxRunSeconds = 0;
            MyBGJobParms.BGJobParm1 = MyRtnFromServiceParms.passedEnterpriseId;
            MyBGJobParms.BGJobParm2 = MyRtnFromServiceParms.passedUserId;
            MyBGJobParms.BGJobTransName = MyRtnFromServiceParms.passedCurrentTransId;
            MyBGJobParms.BGJobTransSeq = MyRtnFromServiceParms.passedCurSeq;
            BGWorker MyBGWorker = new BGWorker();

            // Pass BGWorker & BGWorker Parameters to Background job 
            MyBGWorker.ReceiveMyBGWorker(MyBGWorker);
            MyBGWorker.ReceiveMyBGJobParms(MyBGJobParms);

            // Pass MyWebForm1 to Background job to enable call back with results 
            WebForm1 MyWebForm1 = HttpContext.Current.Handler as WebForm1;
            MyBGWorker.ReceiveMyWebForm1(MyWebForm1);

            // Call Background Job
            MyBGWorker.StartBackgroundProcess(MyBGJobParms);
        }

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        public void StartBackgroundProcess(BGJobParms MyBGJobParms)
        {
            try
            {
                if (MyGlobals.logger2 == null)
                {
                    MyGlobals.logger2 = new LoggerConfiguration()
                   .ReadFrom.AppSettings()
                   .CreateLogger();
                    Log.Logger = MyGlobals.logger2;
                }
                MyGlobals.logger2.Information("START BGJ:   Enterprise: {Enterprise} User: {UserName} Trans: {Trans}  Seq: {Seq} Action: {action} MaxTime {Max} ",  MyBGJobParms.BGJobParm1, MyBGJobParms.BGJobParm2, MyBGJobParms.BGJobTransName, MyBGJobParms.BGJobTransSeq, MyBGJobParms.BGJobAction, MyBGJobParms.BGJobMaxRunSeconds);

            }

            catch (Exception ex)
            {

                MyGlobals.logger2.Error("START BGJ2: { BackgroundCancelError}  Enterprise: {Enterprise} User: {UserName} Trans: {Trans}  Seq: {Seq} Action: {action} MaxTime {Max} ", ex.Message.ToString(),MyBGJobParms.BGJobParm1, MyBGJobParms.BGJobParm2, MyBGJobParms.BGJobTransName, MyBGJobParms.BGJobTransSeq, MyBGJobParms.BGJobAction, MyBGJobParms.BGJobMaxRunSeconds);

            }

            // Create a background worker thread that ReportsProgress &
            // SupportsCancellation
            // Hook up the appropriate events.

            bg_Worker = new BackgroundWorker();
            bg_Worker.DoWork += new DoWorkEventHandler(bg_Worker_DoWork);
            bg_Worker.ProgressChanged += new ProgressChangedEventHandler
                    (bg_Worker_ProgressChanged);
            bg_Worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bg_Worker_RunWorkerCompleted);
            bg_Worker.WorkerReportsProgress = true;
            bg_Worker.WorkerSupportsCancellation = true;

            //
            // Start Background job
            //
            bg_Worker.RunWorkerAsync(MyBGJobParms);  // Call backgroundWorker with list of jobs to run MyBGJobParms parameter is accepted as e.Arguement
        }

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