Google assistant not working in MK81.0-gucci-201809140637-NIGHTLY

I am using MK81.0-gucci-201809140637-NIGHTLY on my Redmi note 1s ( Gucci ), in this rom the Google assistant is not working when ever I tap on “from any screen access of assistant” options it shows a message saying " the Google app is’t your default assist app " even it is already set as default assist app.
Here are in this screenshot and please help.

in my case device gets laggy after installing rom…i have headphone symbol issue tooo. please help