Laravel：雄辩的关系突然停止了工作

After a recent update to my live environment, I got some errors about case sensitive model names that were not found but I fixed those quite fast. Now, after about a week after this update I suddenly receive errors about "property of non object" while trying to access related objects. Here are my models:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class products extends Model {
    /**
     * The table associated with the model.
     *
     * @var string
     */
    protected $table = 'v_products_2';
}

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class order extends Model {
    /**
     * The table associated with the model.
     *
     * @var string
     */
    protected $table = 'v_customers_orders';

    public function getProduct (){
        return $this->belongsTo('App\products', 'product_id', 'product_id');
    }   
}

I've setup my routes and middlewares correctly and after trying to access a property like this will result in an "non-object" error:

echo $orders->getProduct->product_id;

However this exact same code worked like 2 hours ago and has been working for several months now. Except that, this code also works on my Windows Homestead environment making it very hard for me to troubleshoot it. The only way I was able to reproduce this error locally, was to remove the getProduct function from the model. But on live, I get the same behaviour either way.