toolbar button disappearing when dialog closed

Question

my app is fairly simple and always works IF my IOT device is up.
i need to load a popup and show the ReScan button on the toolbar if the device cannot be found.

the app preloads IPaddress="-" and loads 2 asyncTask(s)
one uses NsdManager.DiscoveryListener to find the mDNS name and loads the IP into IPaddress this task watches to see IPaddress change and gets the presets from the device by JSON and sets up the UI or pops up the error dialog with instructions if not found.

MY PROBLEM: when counter >= 15 , i show the "Rescan" Button on the toolbar with setMenuVisible() then popup the error dialog but when the button in the dialog is pressed to close the dialog, the "Rescan" Button disappears again.
Also times out in about 5 seconds.

how do i get the "Rescan" Button to stay?

.

private  class getSettingsFromClock extends AsyncTask<Void, Void, Void> {
  @Override
  protected Void doInBackground(Void... params) {
     String mlooper = IPaddress;
     Log.i(TAG, "LOG getSettingsFromClock doInBackground started ");
     int counter = 0;
     while ( mlooper.equals("-")   ) {
        mlooper = IPaddress;
        try {
            Thread.sleep(600);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        counter++;
        if (counter >= 15)  // in normal operation counter never goes above 3
        {
          Log.i(TAG, "LOG getSettingsFromClock - NO IP Found, count= " + counter );

          runOnUiThread(new Runnable() {
          @Override
          public void run() {

            setMenuVisible( true, R.id.action_rescan);  // show rescan button on toolbar

            try {       // delay is debugging only
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            //scanning failed Popup Dialog
            final Dialog dialog = new Dialog(context );
            dialog.setContentView(R.layout.popup);
            dialog.setTitle("Scan Error");

            Button button = dialog.findViewById(R.id.Button01);
            button.setOnClickListener(new OnClickListener() {
               @Override
               public void onClick(View view) {
                    dialog.dismiss();
               }
            });
            dialog.show();

              Toast.makeText(getApplicationContext(),
                "Could Not get presets from clock. \n check Clock is on and on WiFi\n and reload app.",
              Toast.LENGTH_LONG).show();
           }
          });
               break;
        }
     }
     if( IPaddress != "-" )
     {
       // gets JSON here
     } else
     {
       // add popup - IOT Not found
     }

     // JSON starts here
     if (JSON_return != null) {
            try {
                // loads presets from JSON to UI here
            } catch (final JSONException e) {
                Log.e(TAG, "LOG, JSON parsing error: " + e.getMessage());
            }
     } else 
    {
      Log.e(TAG, "LOG, Could Not get JSON from Clock.");
    }
   return null;
  }
}  // end asyncTask class


 // remember to run on main thread
 // NOTE; private Menu option_Menu; declared in MainActivity
 //  ie;   setMenuVisible( true, R.id.action_rescan);
 public void setMenuVisible(boolean visible, int id) {
   if (option_Menu != null) {
     option_Menu.findItem(id).setVisible(visible);
   }
 }

Answer 1

Mike M. had it, Thank You Mike
   added onPrepareOptionsMenu()
   added showRescan = visible; and invalidateOptionsMenu(); to setMenuVisible()
all work perfectly now.

   @Override
   public boolean onPrepareOptionsMenu(Menu menu) {
     super.onPrepareOptionsMenu(menu);
      try {
         if( showRescan )
         {
            option_Menu.findItem(R.id.action_rescan).setVisible( true );
         } else
         {
            option_Menu.findItem(R.id.action_rescan).setVisible( false );
         }
      }
        catch(Exception e) {
            Log.e(TAG, "onPrepareOptionsMenu error");
        }
     return true;
    }

  // when task is completed you can show your menu just by calling this method
  // remember to run on main thread
  //  ie;   setMenuVisible( true, R.id.action_rescan);
  public void setMenuVisible(boolean visible, int id) {
      if (option_Menu != null) {
         option_Menu.findItem(id).setVisible(visible);
         showRescan = visible;
         invalidateOptionsMenu();
     }
 }