QUdpSocket only receives the first 2 datagrams

Question

I wrote a program for transmitting pictures via UDP in Qt. I encountered a problem that QUdpSocket does not accept an image larger than 50 kb. I decided to split the image into several datagrams and send it. As a result, the required number of datagrams is sent, and, as I understand it, only the first two are received. Why is this happening and do you have other options to solve the problem?

main.cpp:

#include <QApplication>

#include "udp_server.h"
#include "udp_client.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    UDP_Server server(2323);
    UDP_Client client(2323);

    server.show();
    client.show();

    return a.exec();
}

udp_server.h and udp_server.cpp:

#ifndef UDP_SERVER_H
#define UDP_SERVER_H

#include <QWidget>
#include <QUdpSocket>
#include <QBoxLayout>
#include <QLabel>
#include <QBuffer>
#include <QFile>

class UDP_Server : public QWidget
{
    Q_OBJECT
public:
    explicit UDP_Server(int port, QWidget *parent = nullptr);

private:
    QUdpSocket* socket;
    QLabel* showLabel;


private slots:
    void slotProcessDatagrams();

};

#endif // UDP_SERVER_H

//================================

#include "udp_server.h"

UDP_Server::UDP_Server(int port, QWidget *parent)
    : QWidget{parent}
{
    setWindowTitle("SERVER");

    socket = new QUdpSocket(this);
    socket->bind(QHostAddress::LocalHost, port);
    connect(socket, SIGNAL(readyRead()), SLOT(slotProcessDatagrams()));

    showLabel = new QLabel;

    QVBoxLayout* box = new QVBoxLayout;
    box->addWidget(showLabel);
    setLayout(box);
}

void UDP_Server::slotProcessDatagrams() {
    QByteArray datagram;
    QPixmap frame;

    while (socket->hasPendingDatagrams()) {
        QByteArray receivedData;
        receivedData.resize(socket->pendingDatagramSize());
        socket->readDatagram(receivedData.data(), receivedData.size());
        datagram.append(receivedData);
        qDebug() << "read: " << receivedData.size();
    }

    if (frame.loadFromData(datagram, "PNG")) {
        showLabel->setPixmap(frame);
    } else {
        qDebug() << "Failed to read frame";
    }
}

udp_client.h and udp_client.cpp:

#ifndef UDP_CLIENT_H
#define UDP_CLIENT_H

#include <QWidget>
#include <QUdpSocket>
#include <QPushButton>
#include <QBoxLayout>
#include <QTextEdit>
#include <QBuffer>
#include <QFile>

class UDP_Client : public QWidget
{
    Q_OBJECT
public:
    explicit UDP_Client(int port, QWidget *parent = nullptr);

private:
    QUdpSocket* socket;
    int port;

private slots:
    void slotSendDatagram();

};

#endif // UDP_CLIENT_H

//================

#include "udp_client.h"

UDP_Client::UDP_Client(int port, QWidget *parent)
    : QWidget{parent}, port(port)
{
    setWindowTitle("CLIENT");

    socket = new QUdpSocket(this);

    QPushButton* btn = new QPushButton("Send");
    connect(btn, SIGNAL(clicked()), SLOT(slotSendDatagram()));

    QVBoxLayout* box = new QVBoxLayout;
    box->addWidget(btn);
    setLayout(box);

}

const int UDP_DATAGRAM_SIZE = 50000;

void UDP_Client::slotSendDatagram() {
    QFile file("path/to/image");
    if (file.open(QIODevice::ReadOnly)) {
        while (!file.atEnd()) {
            QByteArray datagram = file.read(UDP_DATAGRAM_SIZE);
            socket->writeDatagram(datagram, QHostAddress::LocalHost, port);
            qDebug() << "send: " << datagram.size();
        }
        file.close();
    }

}

output from qDebug():

send: 50000
send: 50000
send: 50000
send: 24753

read: 50000
read: 50000
Failed to read frame

Also, if you try to send a picture weighing less than 50 kb or more than 50 kb but less than 100 kb (to make 2 datagrams), then everything is sent and received normally