Why Hindi italic font not support in mPdf?

Question

I am using mPdf Library with CodeIgniter 3 for Generating dynamic pdf.

i am using below configuration for generating Pdf.

$mpdf = new \Mpdf\Mpdf([
'mode' => 'utf-8',
'format' => $pdf,
'orientation' => $orientation,
'default_font_size' => 54,
'margin_right' => 15,
'margin_left' => 15,
'margin_top' => 15,
'margin_bottom' => 15,
'fontDir' => array_merge($fontDirs, [
$_SERVER["DOCUMENT_ROOT"] . '/assets/fonts/Montserrat',
$_SERVER["DOCUMENT_ROOT"] . '/assets/fonts/OpenSans',
$_SERVER["DOCUMENT_ROOT"] . '/assets/fonts/NotoSerifDevanagari'
]),
'fontdata' => $fontData + [
'montserrat' => [
'R' => 'Montserrat-Regular.ttf',
'I' => 'Montserrat-Italic.ttf',
'B' => 'Montserrat-Bold.ttf',
'BI' => 'Montserrat-BoldItalic.ttf'
],
'opensans' => [
'R' => 'OpenSans-Regular.ttf',
'I' => 'OpenSans-Italic.ttf',
'B' => 'OpenSans-Bold.ttf',
'BI' => 'OpenSans-BoldItalic.ttf'
],
'notoserifdevanagari' => [
'R' => 'NotoSerifDevanagari-Regular.ttf',
'I' => 'NotoSerifDevanagari-Regular.ttf',
'B' => 'NotoSerifDevanagari-Bold.ttf',
'BI' => 'NotoSerifDevanagari-Bold.ttf'
                        ]
],
'default_font' => 'opensans'
]);
$mpdf->jSWord = 1;
$mpdf->autoScriptToLang = true;
$mpdf->baseScript = 1;
$mpdf->autoLangToFont = true;
$mpdf->debug = true;
$mpdf->list_marker_offset='20pt';
$mpdf->list_symbol_size='20pt';
$mpdf->list_indent_default='70pt'; 
$mpdf->WriteHTML($html);

The main issue with Hindi font all type font showing properly but Hindi Italic font not showing properly. I tried many options but not get success. please give me best solution for this. is there any issue with my configuration or library my mPdf library version is 8.0.

Thanks & Regards Lalit