PubNub Arduino subscribe

Hi I am using the PubNubsubscriber example from https://github.com/pubnub/arduino I can receive messages and as long as I receive the message everything works fine, if some time elapses after 20 seconds without a new message, arduino seems to be freezes when "waiting for message (subscribe)" and cannot receive new incoming messages

Does anyone know why this is happening?

  /*
  PubNub sample subscribe client

  This sample client will subscribe to and handle raw PubNub messages
  (not doing any JSON decoding).  It does so with a randomly generated
  UUID.

  Circuit:
  * Ethernet shield attached to pins 10, 11, 12, 13
  * (Optional.) LED on pin 8 for reception indication.
  * Pin A4 unconnected (noise source for random number generator)

  created 23 October 2012
  by Petr Baudis

  https://github.com/pubnub/pubnub-api/tree/master/arduino
  This code is in the public domain.
  */

  #include <SPI.h>
  #include <Ethernet.h>
  #include <PubNub.h>

// Some Ethernet shields have a MAC address printed on a sticker on the shield;
// fill in that address here, or choose your own at random:
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

const int subLedPin = 8;

char pubkey[] = 
char subkey[] = 
char channel[] = "hello_world";
char uuid[] = "xxxxxxxx-xxxx-4444-9999-xxxxxxxxxxxx";

void random_uuid() {
    randomSeed(analogRead(4) + millis() * 1024);
    snprintf(uuid, sizeof(uuid), "%04lx%04lx-%04lx-4444-9999-%04lx%04lx%04lx",
        random(0x10000), random(0x10000), random(0x10000),
        random(0x10000), random(0x10000), random(0x10000));
}

void setup()
{
    pinMode(subLedPin, OUTPUT);
    digitalWrite(subLedPin, LOW);

    Serial.begin(9600);
    Serial.println("Serial set up");

    while (!Ethernet.begin(mac)) {
        Serial.println("Ethernet setup error");
        delay(1000);
    }
    Serial.println("Ethernet set up");

    PubNub.begin(pubkey, subkey);
    random_uuid();
    PubNub.set_uuid(uuid);
    Serial.println("PubNub set up");
}

void flash(int ledPin)
{
    /* Flash LED three times. */
    for (int i = 0; i < 3; i++) {
        digitalWrite(ledPin, HIGH);
        delay(100);
        digitalWrite(ledPin, LOW);
        delay(100);
    }
}

void loop()
{
    Ethernet.maintain();

    PubSubClient *client;

    Serial.println("waiting for a message (subscribe)");
    client = PubNub.subscribe(channel);
    if (!client) {
        Serial.println("subscription error");
        delay(1000);
        return;
    }
    Serial.print("Received: ");
    while (client->wait_for_data()) {
        char c = client->read();
        Serial.print(c);
    }
    client->stop();
    Serial.println();
    flash(subLedPin);

    delay(200);
   }