I also saw another message in debug showing wordpress database error: Lost connection to MySQL server during query SELECT option_value FROM pc3n_options WHERE option_name = ‘jpsq_sync_checkout’ made by shutdown_action_hook, do_action(‘shutdown’), WP_Hook->do_action , WP_Hook->apply_filters, Automattic\Jetpack\Sync\Sender->do_sync, Automattic\Jetpack\Sync\Dedicated_Sender::spawn_sync, Automattic\Jetpack\Sync\Queue->is_locked, Automattic\Jetpack\Sync\Queue->get_checkout_id
OK! I have sent the website URL through support.