The constructor for WP_Customize_Widgets has this bit of code before it does the add_action() and add_filter() calls:

// Skip useless hooks when the user can't manage widgets anyway.
if ( ! current_user_can( 'edit_theme_options' ) ) {
    return;
}

This will cause a problem for previewing widgets on the frontend for unauthenticated users because these filters/actions aren't getting added: https://github.com/xwp/wordpress-develop/blob/885d38edc8de04c3cf7baced5ef0effc8c5a6bd6/src/wp-includes/class-wp-customize-widgets.php#L101-L120

Snapshots should be adding these filters and actions (as required) if ! has_filter() or ! has_action().