OnCharacteristicRead in android does not always respond to changes in characteristics in arduino. What is the problem?

Question

Android

Colleagues, such a problem:
There is a Curie Nano board, there is a phone with android 5.0+. They communicate via Bluetooth Low Energy.
As planned, Curie Nano should periodically transmit 3 parameters (characteristics) to the phone. Here is the code currently on the board:

#include <CurieBLE.h> 

BLEPeripheral blePeripheral; 
BLEService uartService = BLEService("6e400001-b5a3-f393-e0a9-e50e24dcca9e"); 
BLECharacteristic temperatureInsideString = BLECharacteristic("6e400002-b5a3-f393-e0a9-e50e24dcca9e", BLENotify, 20); // температура одежды
BLECharacteristic temperatureOutsideString = BLECharacteristic("6e400003-b5a3-f393-e0a9-e50e24dcca9e", BLENotify, 20); // температура окружающей среды
BLECharacteristic batteryString = BLECharacteristic("6e400004-b5a3-f393-e0a9-e50e24dcca9e", BLENotify, 20); // от 0 до 100

long previousMillis = 0;
byte buff[20]; 
String tempInside; 
String tempOutside;
String battery; 

void setup () { 
  Serial.begin(9600); 
 
  blePeripheral.setLocalName("temperature"); 
  blePeripheral.setAdvertisedServiceUuid(uartService.uuid()); 
  
  blePeripheral.addAttribute(uartService); 
  blePeripheral.addAttribute(temperatureInsideString); 
  blePeripheral.addAttribute(temperatureOutsideString); 
  blePeripheral.addAttribute(batteryString);

  blePeripheral.begin(); 
} 

void loop () { 
  BLECentral central = blePeripheral.central(); 

   if ( central ) { 
    while ( central.connected() ) { 
      long currentMillis = millis(); 
      if ( currentMillis - previousMillis >= 3000 ) { 
        previousMillis = currentMillis; 
        updateTemperature(); 
      } 
    } 
  } 
} 

void updateTemperature () { 
  tempInside = getInsideTemp(); 
  tempInside.getBytes(buff, 20);
  temperatureInsideString.setValue((unsigned char*)buff, 20);  
    
  tempOutside = getOutsideTemp(); 
  tempOutside.getBytes(buff, 20); 
  temperatureOutsideString.setValue((unsigned char*)buff, 20); 

  battery = getBattery();
  battery.getBytes(buff, 20);
  batteryString.setValue((unsigned char*)buff, 20); 
} 

String getInsideTemp () { 
  return (String)36.6; 
} 

String getOutsideTemp () { 
  return (String)-20.0; 
}

String getBattery () { 
  return (String)50; 
}

All characteristics are successfully filled with parameters every 3 seconds, I output them to the port for verification.
From the android side, when the onServicesDiscovered event occurs, I set descriptors to these parameters in order to catch notifications about their changes. Under the debug you can see that the descriptors are put down successfully. Here is the code:

@Override
        public void onServicesDiscovered(BluetoothGatt gatt, int status) {
            if (status == BluetoothGatt.GATT_SUCCESS) {
                BluetoothGattService service = gatt.getService(Constants.TEMP_SERVICE_UUID);
                if (service != null) {
                    BluetoothGattCharacteristic characteristicInsideTemp = service.getCharacteristic(Constants.INSIDE_TEMP_UUID);
                    if (characteristicInsideTemp != null) {
                        setCharacteristicNotification(characteristicInsideTemp, true);
                    }
                    BluetoothGattCharacteristic characteristicOutsideTemp = service.getCharacteristic(Constants.OUTSIDE_TEMP_UUID);
                    if (characteristicOutsideTemp != null) {
                        setCharacteristicNotification(characteristicOutsideTemp, true);
                    }
                    BluetoothGattCharacteristic characteristicBattery = service.getCharacteristic(Constants.BATTERY_UUID);
                    if (characteristicBattery != null) {
                        setCharacteristicNotification(characteristicBattery, true);
                    }
                }
            } else {
                Log.w(TAG, "onServicesDiscovered received: " + status);
            }
        }

    public void setCharacteristicNotification(BluetoothGattCharacteristic characteristic,
                                              boolean enabled) {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.setCharacteristicNotification(characteristic, enabled);

        if (enabled) {
            for (BluetoothGattDescriptor descriptor : characteristic.getDescriptors()) {
                descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
                mBluetoothGatt.writeDescriptor(descriptor);
            }
        }
    }

After executing this code, the onCharacteristicRead callback is executed every 3 seconds, but only 1 characteristic with UUID = 6e400002-b5a3-f393-e0a9-e50e24dcca9e comes there, nothing comes for other characteristics.
On the board, I tried to send different characteristics in turn with an interval of 3 seconds, on the android the result did not change at all.
What could be the problem?

Answer 1

Understood the problem. I set the value of the descriptors in a row, but I had to wait for the onDescriptorWrite callback to fire and only after that set the value of the next descriptor.