ESP8266 SparkFun WiFi Shield UDP package receiving

Recently I bought a SparkFun ESP8266 Wifi Shield. It requires the use of their own library and now I am struggling to receive UDP packages.

Here’s the code that I’m using:

#include <Arduino.h>
#include <SoftwareSerial.h>
#include <SparkFunESP8266WiFi.h>
#include <WiFiUdp.h>

const char ssid[] = "ssid";
const char ps[] = "password";
WiFiUDP Udp;
IPAddress myIP;
char packetBuffer[255];
unsigned const int localPort = 20777;

void setup() {
  Serial.begin(9600);
  Serial.println("Starting setup...");

  if(esp8266.begin()){
    Serial.println("ESP ready to go");
  } else {
    Serial.println("Cannot communicate with esp shield");
  }

  int retVal;
  retVal = esp8266.connect(ssid, ps);
  if(retVal < 0){
    Serial.print(F("Error connecting: "));
    Serial.println(retVal);
  } else {
    myIP = esp8266.localIP();
    Serial.print(F("The IP-address is: ")); Serial.println(myIP);
  }

  Udp.begin(localPort);
  Serial.print("Listening on "); Serial.print(myIP); Serial.print(":"); Serial.println(localPort);
  Serial.println("Waiting for incoming packages...");
}

void loop() {
  int packetSize = Udp.parsePacket();
  if (packetSize) {
    Serial.print("Received packet of size ");
    Serial.println(packetSize);
    Serial.print("From ");
    IPAddress remoteIp = Udp.remoteIP();
    Serial.print(remoteIp);
    Serial.print(", port ");
    Serial.println(Udp.remotePort());

    // read the packet into packetBufffer
    int len = Udp.read(packetBuffer, 255);
    if (len > 0) {
      packetBuffer[len] = 0;
    }
    Serial.println("Contents:");
    Serial.println(packetBuffer);
  }
}

When I boot up WireShark and check the traffic between the sender (local pc) and the receiver (WifiShield), I can see that I’m getting an error:

The provided code does not have any errors.