Job Format does not pass constructor data to Handler

Question

When dispatching a job in Laravel 5.6, send parameters to it. In the constructor, the parameters are received normally, containing the data sent. However, when executing the job with the php artisan queue:work, one of the parameters is empty in Handler.

Code that dispatches the job:

public function enviar($id) {
    $evento = Evento::find($id);
    $subscribers = ParticipantesEvento::join('users', 'participantes_eventos.user_id', '=', 'users.id')
               ->select('users.name', 'users.email')
               ->where('evento_id', '=', $evento->id)
               ->get();
    $certificate = Certificado::where('evento_id', '=', $evento->id)->first();

    dispatch(new SendCertificatesByEmail($subscribers, $evento, $certificate));

    return redirect()->back()->with('success', 'Processando...');
}

Follow the (simplified) job code:

namespace App\Jobs;
use Illuminate\Bus\Queueable;
use Illuminate\Queue\SerializesModels;
use Illuminate\Queue\InteractsWithQueue;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Foundation\Bus\Dispatchable;

class SendCertificatesByEmail implements ShouldQueue {

    use Dispatchable, InteractsWithQueue, Queueable, SerializesModels;

    protected $subscribers, $events, $certificate;

    public function __construct($s, $e, $c) {
        $this->subscribers = $s;
        $this->evento      = $e;
        $this->certificate = $c;

        print_r($this->subscribers);   // Tem dados
        print_r($this->evento);        // Tem dados
        print_r($this->certificate);   // Tem dados
    }

    public function handle() {
        print_r($this->subscribers);    // VAZIO!!!
        print_r($this->evento);         // Tem dados
        print_r($this->certificate);    // Tem dados
    }
}

In the Laravel documentation, it is directed to declare the variables in the job as "protected", as I am doing. Even so, I have tried using them as "public". Same problem. Moreover, only one of the variables "becomes" empty in Handler. Any hint??