laravel collection is 'broken' (strange dots)

I faced this problem before, but couldn't find out the reason. I use laravel 5.5 and php7.0 . I'm fetching data from excel file(about 400 lines) with this excel package(it takes a little bit long to execute the string). the problem is, when I got the collection of data, its kinda 'broken'. what does this mean? I'm sure its not about the package, I had similar problem before when I was making API request, it seems like this problem happens only with big amount of data. can someone explain why this happens and how should fix it? here's my file fetching method

public function index()
{
    \Excel::load('uploads/data.xlsx', function($reader) {
        $results = $reader->all();

        dd($results->all());
    });
}

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