Shopware 6 scheduled task not running

I don't get a scheduled task to run in my module. I followed the documentation:

https://docs.shopware.com/en/shopware-platform-dev-en/how-to/scheduled-tasks

and:

https://docs.shopware.com/en/shopware-platform-dev-en/references-internals/core/module/tasks

But it seems the task never runs (I added logging to make sure). The task is showing up in the 'scheduled_task' database table with the status 'queued' and a last_execution_time of 'NULL'. It looks like the other scheduled tasks (like the delete_newsletter_recipient_task, requeue_dead_messages, product_export_generate_task, shopware.sitemap_generate and shopware.elasticsearch.create.alias) are running however. Also if I manualy run the 'DownloadFeedTaskHandler' 'run' method the code is working as expected.

I found this (German) forum post with more or less the same problem, but no solution:

https://forum.shopware.com/discussion/67988/scheduled-task-hat-den-queued-status

I checked the dead_messages table but it doesn't have any records.

Any idea how to go from here?

My relevant files look like:

custom/plugins/AWSamplePlugin/src/Resources/config/services.xml:

<?xml version="1.0" ?>
<container xmlns="http://symfony.com/schema/dic/services"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">
    <services>
        <service id="AW\SamplePlugin\ScheduledTask\DownloadFeedTask">
            <tag name="shopware.scheduled.task" />
        </service>
        <service id="AW\SamplePlugin\ScheduledTask\DownloadFeedTaskHandler">
            <argument type="service" id="scheduled_task.repository" />
            <argument type="service" id="Shopware\Core\System\SystemConfig\SystemConfigService" />
            <argument type="service" id="logger" />
            <argument type="service" id="sales_channel.repository" />
            <tag name="messenger.message_handler" />
        </service>
    </services>
</container>

custom/plugins/AWSamplePlugin/src/ScheduledTask/DownloadFeedTask.php:

<?php declare(strict_types=1);

namespace AW\SamplePlugin\ScheduledTask;

use Shopware\Core\Framework\MessageQueue\ScheduledTask\ScheduledTask;

class DownloadFeedTask extends ScheduledTask
{
    public static function getTaskName(): string
    {
        return 'aw.download_feed';
    }

    public static function getDefaultInterval(): int
    {
        return 60; // Every minute
    }
}

custom/plugins/AWSamplePlugin/src/ScheduledTask/DownloadFeedTaskHandler.php:

<?php declare(strict_types=1);

namespace AW\SamplePlugin\ScheduledTask;

use Shopware\Core\Framework\MessageQueue\ScheduledTask\ScheduledTaskHandler;
use Shopware\Core\Framework\DataAbstractionLayer\EntityRepositoryInterface;
use Shopware\Core\System\SystemConfig\SystemConfigService;
use Psr\Log\LoggerInterface;

class DownloadFeedTaskHandler extends ScheduledTaskHandler
{
    protected $systemConfigService;
    protected $logger;
    protected $salesChannelRepository;

    public function __construct(
        EntityRepositoryInterface $scheduledTaskRepository,
        SystemConfigService $systemConfigService,
        LoggerInterface $logger,
        EntityRepositoryInterface $salesChannelRepository
    ) {
        $logger->info('__construct');
        parent::__construct($scheduledTaskRepository);
        $this->systemConfigService = $systemConfigService;
        $this->logger = $logger;
        $this->salesChannelRepository = $salesChannelRepository;
        $logger->info('__construct END');
    }

    public static function getHandledMessages(): iterable
    {
        return [ DownloadFeedTask::class ];
    }

    public function run(): void
    {
        $this->logger->info('RUNNING!');
        echo "ScheduledTask run";
    }
}