Problem with generate multiple file mPDF codeigniter - codeigniter

Question

Hello guys i'm a little bit confuse with my mpdf function in codeigniter to generate multiple file pdf, i tried to research and nothing can solve this is issue,
i have anchor that action to download function, and the idea is to call all function with mpdf generate in it. here is the code :
public function download($id)
{
$this->kehadiranDosen($id);
$this->nilaiSeminar($id);
$this->beritaAcara($id);
}
function beritaAcara($id)
{
$data['peserta'] = $this->db->get_where('seminar', ['id' => $id])->row_array();
//Berita Acara
$html = $this->load->view('seminar/beritaAcara', $data, true);
$this->load->library('M_pdf');
$mpdf = $this->m_pdf->load([
'mode' => 'utf-8',
'format' => 'A4'
]);
$mpdf->WriteHTML($html);
$mpdf->Output('BERITA ACARA,' . ucfirst($data['peserta']['nama']) . ',' . $data['peserta']['npm'] . '.pdf', "I");
unset($mpdf);
unset($html);
}
function kehadiranDosen($id)
{
$data['peserta'] = $this->db->get_where('seminar', ['id' => $id])->row_array();
//Kehadiran Dosen
$html2 = $this->load->view('seminar/kehadiranDosen', $data, true);
$this->load->library('M_pdf');
$mpdf2 = $this->m_pdf->load([
'mode' => 'utf-8',
'format' => 'A4'
]);
$mpdf2->WriteHTML($html2);
$mpdf2->Output('KEHADIRAN DOSEN,' . ucfirst($data['peserta']['nama']) . ',' . $data['peserta']['npm'] . '.pdf', "I");
unset($mpdf2);
unset($html2);
}
function nilaiSeminar($id)
{
$data['peserta'] = $this->db->get_where('seminar', ['id' => $id])->row_array();
//Nilai Seminar
$html3 = $this->load->view('seminar/nilaiSeminar', $data, true);
$this->load->library('M_pdf');
$mpdf3 = $this->m_pdf->load([
'mode' => 'utf-8',
'format' => 'A4'
]);
$mpdf3->WriteHTML($html3);
$mpdf3->Output('NILAI SEMINAR,' . ucfirst($data['peserta']['nama']) . ',' . $data['peserta']['npm'] . '.pdf', "I");
unset($mpdf3);
unset($html3);
}
and when i click it, only kehadiran dosen generated, anyone can solve this? thank you so much before