mystery checkbox in comments area

This is to respect the new (May 25 2018) European Union law “The General Data Protection Regulation” (GDPR).

When checkbox is checked, it says the browser to save the name, email and website in the cookie to reuse them later.

When comment form <label> is CSS-styled the right way, the label text “Save my name, email, and website in this browser for the next time I comment.” it visible. Also you can inspect it in Developer Tools like you’ve done with <input>.

If you are not affected by GDPR, simply remove the checkbox putting the following code in your theme’s functions.php:

add_filter( 'comment_form_default_fields', 'comment_form_hide_cookies_consent' );

function comment_form_hide_cookies_consent( $fields )
{
    unset( $fields['cookies'] );
    return $fields;
}