CI3.1.7 Upload Image Sometime Failed

Hello,

I found some strange thing.
I have two images, but I can only upload one of them.
https://ibb.co/j1U0yb

I can upload 456.jpg,
but I can't upload 123.jpg (it will upload noimage.jpg instead)

This is my controller's code

PHP Code:

$config['upload_path'] = './assets/images/event/';
$config['allowed_types'] = 'gif|jpg|png|jpeg';
$config['max_size'] = '2048';
$config['max_width'] = '1500';
$config['max_height'] = '1500';
$config['remove_spaces'] = FALSE;

$this->load->library('upload', $config);
if(!$this->upload->do_upload('userfile')){
  $errors = array('error'=> $this->upload->display_errors());
  $post_image = 'noimage.jpg';
}else{
  $data = array('upload_data' => $this->upload->data());
  $post_image = $_FILES['userfile']['name'];
}
$this->Event->create_events($post_image);
$this->session->set_flashdata('event_created','Your event has been created');
redirect('events'); 


Anyone have idea?

Thank you very much in advance.

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