My ESP8266 doesnt automatically connect to WIFI after a router reboot

I just changed to an MI 3C router from a Dlink.
I had to do a router reboot a couple of times and all my ESPs all over the place lost connection. I had to do a physical power on/off to get them all back on line. I believe ESP has a inbuilt auto connect feature ?

Sorry I have a very poor knowledge of coding and bad with English, I am a biotechnologist professional.

I have similar code running on another 12 ESPs doing various things like running Drip Irrigation systems, checking moisture levels etc. This particular one is used to notify me when a bell push button is pressed and toggle a light.

Also if possible please suggest any improvements to the code.

Thanks

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <ESP8266mDNS.h>
#include <WiFiUdp.h>
#include <ArduinoOTA.h>

const char* ssid = "Ven Res";
const char* password = "venhazari";
const char* mqtt_server = "192.168.0.103";

WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
char msg2[50];

int value = 0;
const int Bell = D2;

void setup_wifi() {
  delay(10);
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.persistent(false);
  WiFi.mode(WIFI_OFF);   // this is a temporary line, to be removed after SDK update to 1.5.4
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);


  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  randomSeed(micros());
  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
  }
  Serial.println();

  if ((char)payload[0] == '0') {
    digitalWrite(D1, HIGH);

  } else {
    digitalWrite(D1, LOW);
  }

}

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Create a random client ID
    String clientId = "ESP8266Client-";
    clientId += String(random(0xffff), HEX);
    if (client.connect(clientId.c_str())) {
      Serial.println("connected");
      Serial.println (clientId.c_str());
      client.subscribe("WashLight");
    } else {

      delay(5000);
    }
  }
}

void setup() {
  ArduinoOTA.begin();
  pinMode(Bell, INPUT_PULLUP);
  pinMode(D1, OUTPUT);
  //digitalWrite(D1,HIGH);
  Serial.begin(115200);
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
}
void loop() {
  ipaddress();
  if (!client.connected()) {
    reconnect();
  }
  if (digitalRead(Bell) == LOW) {
    client.publish("BellOut", "Bell Pressed");
    delay (500);
  } else {
    client.publish("BellOut", "Bell Open");
  }

  client.loop();
  long now = millis();
  if (now - lastMsg > 18000) {
    lastMsg = now;
    ++value;
    snprintf (msg, 75, "Bell #%ld", value);
    Serial.print("Publish message: ");
    Serial.println(msg);
    client.publish("Bell_Status", msg);
    sprintf(msg2, "%ld", (2*(WiFi.RSSI()+100)));
    client.publish("Bell", msg2);
  }
  ArduinoOTA.handle();
}

Could this be the problem?

  WiFi.persistent(false);

Or maybe in loop() you should do something like re-connect when (WiFi.status() != WL_CONNECTED).

Can you please elaborate ? Shall I remove this WiFi.persistent(false);

I have noticed an ESP has disconnected even with out a router boot and did not connect back at all until i did a power cycle