artyshake

Deactivating Jetpack did not resolve the error.

P.S. I reinstalled WPForms because we need the Contact form to work. As you will see on the contact page, recaptcha works fine there. However, on product review pages, not only recaptcha is not visible (and it is not installed), but it returns an error.

This is wp-comments-post.php:

<?php
/**
 * Handles Comment Post to WordPress and prevents duplicate comment posting.
 *
 * @package WordPress
 */

if ( 'POST' !== $_SERVER['REQUEST_METHOD'] ) {
	$protocol = $_SERVER['SERVER_PROTOCOL'];
	if ( ! in_array( $protocol, array( 'HTTP/1.1', 'HTTP/2', 'HTTP/2.0' ), true ) ) {
		$protocol = 'HTTP/1.0';
	}

	header( 'Allow: POST' );
	header( "$protocol 405 Method Not Allowed" );
	header( 'Content-Type: text/plain' );
	exit;
}

/** Sets up the WordPress Environment. */
require __DIR__ . '/wp-load.php';

nocache_headers();

$comment = wp_handle_comment_submission( wp_unslash( $_POST ) );
if ( is_wp_error( $comment ) ) {
	$data = (int) $comment->get_error_data();
	if ( ! empty( $data ) ) {
		wp_die(
			'<p>' . $comment->get_error_message() . '</p>',
			__( 'Comment Submission Failure' ),
			array(
				'response'  => $data,
				'back_link' => true,
			)
		);
	} else {
		exit;
	}
}

$user            = wp_get_current_user();
$cookies_consent = ( isset( $_POST['wp-comment-cookies-consent'] ) );

/**
 * Perform other actions when comment cookies are set.
 *
 * @since 3.4.0
 * @since 4.9.6 The <code>$cookies_consent</code> parameter was added.
 *
 * @param WP_Comment $comment         Comment object.
 * @param WP_User    $user            Comment author's user object. The user may not exist.
 * @param bool       $cookies_consent Comment author's consent to store cookies.
 */
do_action( 'set_comment_cookies', $comment, $user, $cookies_consent );

$location = empty( $_POST['redirect_to'] ) ? get_comment_link( $comment ) : $_POST['redirect_to'] . '#comment-' . $comment->comment_ID;

// If user didn't consent to cookies, add specific query arguments to display the awaiting moderation message.
if ( ! $cookies_consent && 'unapproved' === wp_get_comment_status( $comment ) && ! empty( $comment->comment_author_email ) ) {
	$location = add_query_arg(
		array(
			'unapproved'      => $comment->comment_ID,
			'moderation-hash' => wp_hash( $comment->comment_date_gmt ),
		),
		$location
	);
}

/**
 * Filters the location URI to send the commenter after posting.
 *
 * @since 2.0.5
 *
 * @param string     $location The 'redirect_to' URI sent via $_POST.
 * @param WP_Comment $comment  Comment object.
 */
$location = apply_filters( 'comment_post_redirect', $location, $comment );

wp_safe_redirect( $location );
exit;