如果你看看wp_sanitize_redirect() 函数，您会注意到它正在从目标URL中删除新行：

https://core.trac.wordpress.org/browser/tags/4.9/src/wp-includes/pluggable.php#L1249

1-将消息上的新行转换为允许差异的唯一字符组合，然后在从responseMsg URL参数。

2-因为这是pluggable function, 您可以将其放在插件上，并根据需要进行自定义。类似这样：

if ( !function_exists(\'wp_redirect\') ) :
/**
 * Redirects to another page.
 *
 * Note: wp_redirect() does not exit automatically, and should almost always be
 * followed by a call to `exit;`:
 *
 *     wp_redirect( $url );
 *     exit;
 *
 * Exiting can also be selectively manipulated by using wp_redirect() as a conditional
 * in conjunction with the {@see \'wp_redirect\'} and {@see \'wp_redirect_location\'} hooks:
 *
 *     if ( wp_redirect( $url ) ) {
 *         exit;
 *     }
 *
 * @since 1.5.1
 *
 * @global bool $is_IIS
 *
 * @param string $location The path to redirect to.
 * @param int    $status   Status code to use.
 * @return bool False if $location is not provided, true otherwise.
 */
function wp_redirect($location, $status = 302, $strip_new_lines = true) {
    global $is_IIS;

    /**
     * Filters the redirect location.
     *
     * @since 2.1.0
     *
     * @param string $location The path to redirect to.
     * @param int    $status   Status code to use.
     */
    $location = apply_filters( \'wp_redirect\', $location, $status );

    /**
     * Filters the redirect status code.
     *
     * @since 2.3.0
     *
     * @param int    $status   Status code to use.
     * @param string $location The path to redirect to.
     */
    $status = apply_filters( \'wp_redirect_status\', $status, $location );

    if ( ! $location )
        return false;

    $location = wp_sanitize_redirect($location, $strip_new_lines);

    if ( !$is_IIS && PHP_SAPI != \'cgi-fcgi\' )
        status_header($status); // This causes problems on IIS and some FastCGI setups

    header("Location: $location", true, $status);

    return true;
}
endif;

if ( !function_exists(\'wp_sanitize_redirect\') ) :
/**
 * Sanitizes a URL for use in a redirect.
 *
 * @since 2.3.0
 *
 * @param string $location The path to redirect to.
 * @return string Redirect-sanitized URL.
 **/
function wp_sanitize_redirect($location, $strip_new_lines = true) {
    $regex = \'/
        (
            (?: [\\xC2-\\xDF][\\x80-\\xBF]        # double-byte sequences   110xxxxx 10xxxxxx
            |   \\xE0[\\xA0-\\xBF][\\x80-\\xBF]    # triple-byte sequences   1110xxxx 10xxxxxx * 2
            |   [\\xE1-\\xEC][\\x80-\\xBF]{2}
            |   \\xED[\\x80-\\x9F][\\x80-\\xBF]
            |   [\\xEE-\\xEF][\\x80-\\xBF]{2}
            |   \\xF0[\\x90-\\xBF][\\x80-\\xBF]{2} # four-byte sequences   11110xxx 10xxxxxx * 3
            |   [\\xF1-\\xF3][\\x80-\\xBF]{3}
            |   \\xF4[\\x80-\\x8F][\\x80-\\xBF]{2}
        ){1,40}                              # ...one or more times
        )/x\';
    $location = preg_replace_callback( $regex, \'_wp_sanitize_utf8_in_redirect\', $location );
    $location = preg_replace(\'|[^a-z0-9-~+_.?#=&;,/:%!*\\[\\]()@]|i\', \'\', $location);
    $location = wp_kses_no_null($location);

    // remove %0d and %0a from location
    $strip = array(\'%0d\', \'%0a\', \'%0D\', \'%0A\');
    return $strip_new_lines ? _deep_replace( $strip, $location ) : $location;
}

/**
 * URL encode UTF-8 characters in a URL.
 *
 * @ignore
 * @since 4.2.0
 * @access private
 *
 * @see wp_sanitize_redirect()
 *
 * @param array $matches RegEx matches against the redirect location.
 * @return string URL-encoded version of the first RegEx match.
 */
function _wp_sanitize_utf8_in_redirect( $matches ) {
    return urlencode( $matches[0] );
}
endif;

// by default is removing new lines so we pass false
$strip_new_lines = false;
$location = "/upload_success?responseMsg=".urlencode($new_body->message);

// make sure you pass the correct HTTP 
// status here to prevent penalty or any  other SEO issue
$status = 302;

wp_redirect( $location, $status,  $strip_new_lines );
//  wp_redirect() does not exit automatically
exit;