When this happened , I reset my Roku device and starting Relinking and adding Roku to Google Home. It might be sometimes Internet issues - so make sure that is reliable.Check your Roku and Google Home firmware -Whether it is updated or not.Hope that helps !
I have read all the comments and tried to make this work, but try as I might I cannot link roku to my google home. It just spins around and around. Sometimes it says it is linked but it never is. I tried turning off 2fa and it still doesn't work. HELP
Try going to Settings/System/Advanced System Settings/Control by Mobile Apps/Network Access and changing 'Limited' to Permissive or Enabled.