Unable to Run iOS App for more than 30 to 40 seconds even the backgroundtask is integrated

We are integrating Auto-door unlock application for iOS. This app should start scanning for Beacons first, from didRangeBeacons in the region(), we get major & minor value, then we prepare a customized CBUUID Service using

Code Block 
computedService = CBUUID(string: "\(major+minor)-xxxx-xxxx-xxxx-xxxxxxxxxxxx")

and then start scanning for BLE Peripheral

Code Block 
centralManager.scanForPeripherals(withServices: [computedService], options: [CBCentralManagerScanOptionAllowDuplicatesKey: false])

App Launches -->
Start Scanning for iBeacon Region with UUID(uuidString: "{Provided UUID}") only (Minor value will be different)

when

Code Block 
func locationManager(_ manager: CLLocationManager, didRangeBeacons beacons: [CLBeacon], in the region: CLBeaconRegion)

 
callback is received,
we are extracting Major & Minor value from the detected beacon, preparing a Service UUID string based on this value

e.g. if the Major value is: 00 & Minor value is "11", concatenating this will be "0011" and adding this final value as a prefix of device service UUID e.g. "0011-xxxx-xxxx-xxxx-xxxxxxxxxxxx" to start scanning for BLE Peripheral.

So my BLECentralManager object would start scanning as

self?.bleCentralManager.scanForPeripherals(withServices: "0011-xxxx-xxxx-xxxx-xxxxxxxxxxxx", options: [CBCentralManagerScanOptionAllowDuplicatesKey: false])

Once the BLE Peripheral is detected, the rest of the BLE Operations are performed on this peripheral (i.e. Making a connection, sending data to a specific characteristic, and at last Drop the connection).

This works well in foreground mode.

Now, To Run the same operation for "App Not running state / Killed State", I have added the Location manager's didEnterRegion & didExitRegion monitoring.

I am getting a callback when a user enters into the beacon range and sends a local notification too. During this, we have started beacon ranging and initiated background task as below:

Code Block 
func locationManager(_ manager: CLLocationManager, didEnterRegion region: CLRegion) {
        guard region is CLBeaconRegion else { return }
        self.showLocalNotification(title: "Thank you", body: "You're in my region now!")
        manager.startRangingBeacons(in: region as! CLBeaconRegion)
        self.extendBackgroundRunningTime()  
}
// Extending Background Execution Time
func extendBackgroundRunningTime() {
        if (self.backgroundTask != .invalid) {
            return
        }
        self.backgroundTask = UIApplication.shared.beginBackgroundTask(withName: "DummyTask", expirationHandler: {            	
UIApplication.shared.endBackgroundTask(self.backgroundTask)
            self.backgroundTask = .invalid
        })
        if threadStarted {
            print("Background task thread already started.")
        } else {
            threadStarted = true
            DispatchQueue.global(qos: .default).async {
                while (true) {
                    Thread.sleep(forTimeInterval: 1);
                }
            }
        }
}

When beacon ranging identifies the beacon detail, I need to get major, minor value, prepare a CBUUID string (as mentioned above), make a connection, and process door-open operation (for app killed state)

but I am not getting a callback in

Code Block 
func centralManager(_ central: CBCentralManager, didDisconnectPeripheral peripheral: CBPeripheral, error: Error?) 

within 30 seconds time. I have read that backgroundTask can extend app time for 3 minutes. But I am getting 30/40 seconds hardly during iBeacon Ranging and unable to scan the BLE peripheral

Can you please help me how can I achieve the behaviour for Background mode?