How to solve Laravel Pusher Error data content of this event exceeds

Question

I did the update to Laravel 9 today. Before, Pusher worked well on the application.

Now, I receive always the following error:

Pusher error: The data content of this event exceeds the allowed maximum (10240 bytes)

I didn't change the content.

I tested to change the content with the given supplier_id, with a fake id like "ee" and without any restrictions.

In the console log, I have the following result:

Why does pusher work, even there is an error in the backend?

<?php

namespace App\Events\Kanban;

use Illuminate\Broadcasting\InteractsWithSockets;
use Illuminate\Contracts\Broadcasting\ShouldBroadcast;
use Illuminate\Foundation\Events\Dispatchable;
use Illuminate\Queue\SerializesModels;
use Illuminate\Support\Facades\Log;

class KanbanOrderCreatedEvent  implements ShouldBroadcast
{
    use Dispatchable, InteractsWithSockets, SerializesModels;

    public $kanbanOrder;

    public function __construct($kanbanOrder)
    {
        $this->kanbanOrder = $kanbanOrder;
    }

    /**
     * Get the channels the event should broadcast on.
     *
     * @return \Illuminate\Broadcasting\Channel|array
     */
    public function broadcastOn()
    {
        return ['kanbanOrders.'.$this->kanbanOrder->network_supplier_id];
    }

    public function broadcastAs()
    {
        return 'kanbanOrderCreated';
    }

    public function broadcastWith()
    {
        return ['supplier_id' => $this->kanbanOrder->network_supplier_id];
    }

}