Programmatically saving data in a field under user account

QR codes have been printed out for a bunch of students in a university. When they visit the site via those QR codes, and they are logged-in, the refcode query parameter used in the link needs to be saved for their account in a field_usr_ref_code field (a Text (plain) field).

In a .module file I am using the following code.

use Drupal\user\Entity\User;

/**
 * Implements hook_entity_load().
 */
function my_custom_module_entity_load() {
  $refcode = \Drupal::request()->query->get('refcode');
  $user_id = \Drupal::currentUser()->id();
  if ($user_id > '0' && isset($refcode)) {
    $account = User::load($user_id);    
    $account->set('field_usr_ref_code', $refcode);
    $account->save();
  }
}

However, for some reason no data is being saved, without any logged error.

What is wrong with the code I am using?

Use a request event subscriber with a priority of 299:

/src/EventSubscriber/MymoduleSubscriber.php

<?php

namespace Drupal\mymodule\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\KernelEvents;
use Symfony\Component\HttpKernel\Event\RequestEvent;

/**
 * Mymodule event subscriber.
 */
class MymoduleSubscriber implements EventSubscriberInterface {

  /**
   * Kernel request event handler.
   *
   * @param \Symfony\Component\HttpKernel\Event\RequestEvent $event
   *   The request event.
   */
  public function onKernelRequest(RequestEvent $event) {
    if (!$event->isMainRequest()) {
      return;
    }
    // put here your code
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    return [
      KernelEvents::REQUEST => ['onKernelRequest', 299],
    ];
  }
}
   

mymodule.services.yml

services:
  mymodule.event_subscriber:
    class: Drupal\mymodule\EventSubscriber\MymoduleSubscriber
    tags:
      - { name: event_subscriber }

Drupal runs authentication with priority 300.

This code is for Drupal 9/10.

For Drupal 8 you need to use Symfony\Component\HttpKernel\Event\GetResponseEvent and $event->isMasterRequest().