Shortcode not working inside html input

As above, https://wordpress.stackexchange.com/a/195673/22728 solved it:

add_filter( 'wp_kses_allowed_html', function ( $allowedposttags, $context ) {
    if ( $context == 'post' ) {
        $allowedposttags['input']['value'] = 1;
    }
    return $allowedposttags;
}, 10, 2 );