[Plugin: Jetpack by WordPress.com] multisite cannot connect to wordpress.com

Jetpack was working fine on my site: maimaimai.uk until I changed my site to wordpress multisite.

on network admin level, clicked Connect to WordPress.com
it went to this URL:
URL REDACTED

After I clicked Approve, It returned to this URL showing a blank page:

URL REDACTED

On site level, when I click jetpack debug, it shows:

It looks like your site can not communicate properly with Jetpack.
SELF:
	Array
(
    [headers] => Array
        (
            [server] => nginx
            [date] => Thu, 26 Nov 2015 00:31:52 GMT
            [content-type] => text/plain;charset=utf-8
            [connection] => close
            [expires] => Wed, 11 Jan 1984 05:00:00 GMT
            [cache-control] => no-cache, must-revalidate, max-age=60
            [pragma] => no-cache
            [x-hacker] => Jetpack Test
            [x-ac] => 3.lhr _dca
        )

    [body] => {"error":"Could not validate security token","error_description":"We were unable to validate a security token for Jetpack communication. Please try disconnecting Jetpack from your WordPress.com account, and connecting it again."}
    [response] => Array
        (
            [code] => 400
            [message] => Bad Request
        )

    [cookies] => Array
        (
        )

    [filename] =>
)

I have tried to change theme, disable all other plugin, still no luck.

Site: http://maimaimai.uk/
https://wordpress.org/plugins/jetpack/