Won’t connect to xfinity streaming was working 2 weeks ago now it doesn’t says it’s an error
What's the error message and/or code? What's the model number of your Roku device displayed under Settings->System->About?
I'm going to guess that you have a 2.4GHz Wi-Fi model and you need to change your Wi-Fi wireless mode to b/g/n.
Xfinity Stream is Comcast's app - they created it, supplied it to Roku, and maintain it. Roku just supplies the platform on which it runs. Have you contacted Comcast to ask them what changed?