Why doesn't it always connect to esp01 server?

Question

Arduino

there is a code for esp

#include <ESP8266WiFi.h>

#ifndef STASSID
#define STASSID "ssid"
#define STAPSK  "pass"
#endif

const char* ssid = STASSID;
const char* password = STAPSK;
WiFiServer server(80);

void setup() {
  Serial.begin(9600);
 
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }
  server.begin();
}
void loop() {
  WiFiClient client = server.available();
  if (!client) {
    return;
  }
  else
  {
    client.println(F("OK"));
  }
  client.setTimeout(5000); 
  byte* buf;
  while (client)
    while (client.available()) {
     char c = client.read();
     Serial.write(c);
   }
}

I am writing on arduino, because I spit with pluses to mess around, and so I can’t figure it out.
in the router settings, I reserved ip, which was always given locally.
but tcp clients connect every other time and in general everything is unstable.
As far as I know, you don't need a white ip to connect to an esp server on the local network.
what's wrong with him?