Laravel Notification with ShouldQueue: toDatabase store different [data] - laravel

Question

I have ServiceOrderCreated.php notification and want to use ShouldQueue, but it stores notification other than when I don't use ShouldQueue.
These are data sent to ServiceOrderCreated Class:
//notification
class ServiceOrderCreated extends Notification implements ShouldQueue
{
use Queueable;
protected $serviceOrder;
/**
* Create a new notification instance.
*
* #return void
*/
public function __construct(ServiceOrder $serviceOrder)
{
$this->serviceOrder = $serviceOrder;
}
/**
* Get the notification's delivery channels.
*
* #param mixed $notifiable
* #return array
*/
public function via($notifiable)
{
return ['mail', 'database'];
}
/**
* Get the array representation of the notification.
*
* #param mixed $notifiable
* #return json
*/
public function toDatabase($notifiable)
{
//dd($this->serviceOrder);
return [
$this->serviceOrder
];
}
/**
* Get the mail representation of the notification.
*
* #param mixed $notifiable
* #return \Illuminate\Notifications\Messages\MailMessage
*/
public function toMail($notifiable)
{
$message = new MailMessage;
$message->subject('Sportservis-Hostivice: Nová zákazka č. '.$this->serviceOrder->id);
foreach ($this->serviceOrder->serviceOrderItem as $item) {
$message->line('<li>'.$item->customerOrderAsset->name.' - '.$item->serviceType->name.' - '.$item->price.'</li>');
}
return $message;
}
Problem is, that when I remove "implements ShouldQueue", it stores whole collection ($newServiceOrder) to Notifications table ([data] column). When "implements ShouldQueue" is in place, only bare model without relations is stored to Notifications table.
Any idea? Did I miss Something?
UPDATE
This is the collection which is passed from ServiceOrderController.php to notification.
$newServiceOrder = ServiceOrder::with(['serviceOrderItem', 'serviceOrderItem.serviceType', 'serviceOrderItem.customerOrderAsset', 'customer'])->find($serviceOrder->id)
$newServiceOrder->customer->notify(new ServiceOrderCreated($newServiceOrder));
UPDATE 2:
This is what is store in notifications table when I don't use ShouldQueue:
https://pastebin.com/hXF03tEa
And this is what is stored when I use ShouldQueue:
https://pastebin.com/Vb6hFZkH