Because WP core automatically adds noreferrer, noopener in rel attribute on open links, it clears also the attribute mtli_filesize value. Note: My open links are PDF internal files.
Meanwhile, awaiting an update of the plugin, I have modified the file mime_type_link_images.php this way.
On line ~1246 I relplaced
$replace = str_replace( $match[3], $match[3] . ' rel="mtli_filesize' . str_replace( array( '.', ' ' ), '', $filesize ) . '"', $replace );
with
$replace = str_replace( $match[3], $match[3] . ' relmtli="mtli_filesize' . str_replace( array( '.', ' ' ), '', $filesize ) . '"', $replace );
On line ~1254 I replaced
$this->filesize_styles[] = 'a[rel~="mtli_filesize' . str_replace( array( '.', ' ' ), '', $filesize ) . '"]:after {content:" ' . $css_filesize_string . '"}';
with
$this->filesize_styles[] = 'a[relmtli~="mtli_filesize' . str_replace( array( '.', ' ' ), '', $filesize ) . '"]:after {content:" ' . $css_filesize_string . '"}';
It seems to work temporarily.
