ESP32 BLE doesn't reconnect after disconnecting

Hardware Nano Family Nano ESP32
1

Hi,
I'm new to ESP32. I'm now trying out the BLE code to broadcast sine values to my Android 11 phone (I'm doing it natively and not using nrfConnect). However, it doesn't get connected whenever I try to reconnect after disconnecting. I have to forget the device, scan for the device, and then connect to it. Are there any workarounds to this? Any advice for it to work correctly?

/*
  Install "Arduino ESP32 Boards" by Arduino and "esp32" by Espressif Systems
*/

#include <BLE2902.h>
#include <BLEDevice.h>
#include <BLEUtils.h>
#include <BLEServer.h>

BLEServer *pServer = NULL;
BLECharacteristic *pCharacteristic = NULL;
bool deviceConnected = false;
bool oldDeviceConnected = false;
float value = 0;

const float AMP = 1.0; // Amplitude of the sine wave
const float F = 1.0; // Frequency of the sine wave
const int POINTS = 100;  // Number of points in the sine wave


// See the following for generating UUIDs:
// https://www.uuidgenerator.net/

#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"

class MyServerCallbacks : public BLEServerCallbacks {
  void onConnect(BLEServer *pServer) {
    deviceConnected = true;
  };

  void onDisconnect(BLEServer *pServer) {
    deviceConnected = false;
    BLEDevice::stopAdvertising();
    pServer->getAdvertising()->start();
  }
};

void setup() {
  Serial.begin(115200);

  // Create the BLE Device
  BLEDevice::init("ESP32");

  // Create the BLE Server
  pServer = BLEDevice::createServer();
  pServer->setCallbacks(new MyServerCallbacks());

  // Create the BLE Service
  BLEService *pService = pServer->createService(SERVICE_UUID);

  // Create a BLE Characteristic
  pCharacteristic = pService->createCharacteristic(
    CHARACTERISTIC_UUID,
    BLECharacteristic::PROPERTY_READ | BLECharacteristic::PROPERTY_WRITE | BLECharacteristic::PROPERTY_NOTIFY | BLECharacteristic::PROPERTY_INDICATE
  );

  // https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.descriptor.gatt.client_characteristic_configuration.xml
  // Create a BLE Descriptor
  pCharacteristic->addDescriptor(new BLE2902());

  // Start the service
  pService->start();

  // Start advertising
  BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
  pAdvertising->addServiceUUID(SERVICE_UUID);
  pAdvertising->setScanResponse(false);
  pAdvertising->setMinPreferred(0x0);  // set value to 0x00 to not advertise this parameter
  BLEDevice::startAdvertising();
  Serial.println("Waiting a client connection to notify...");
}

void loop() {
  // notify changed value
  if (deviceConnected) {

     // Continuously generate and send sine wave points
    static int i = 0;  // Static variable to keep track of the current point

    // Calculate the angle for the current point
    float angle = (2.0 * PI * i) / POINTS;


    pCharacteristic->setValue((uint8_t *)&value, 4);
    pCharacteristic->notify();
    value =  AMP * sin(F * angle);

    // Print the sine value to Serial (for debugging)
    Serial.println(value);

    // Increment the point index, and wrap around if necessary
    i = (i + 1)%POINTS;

    delay(500);  // bluetooth stack will go into congestion, if too many packets are sent, in 6 hours test i was able to go as low as 3ms
  }
  // disconnecting
  if (!deviceConnected && oldDeviceConnected) {
    delay(500);                   // give the bluetooth stack the chance to get things ready
    pServer->startAdvertising();  // restart advertising
    Serial.println("start advertising");
    oldDeviceConnected = deviceConnected;
  }
  // connecting
  if (deviceConnected && !oldDeviceConnected) {

    oldDeviceConnected = deviceConnected;
  }
}