After switching bridge mode to eliminate our router and use the xFinity router, my wife can't access certain web sites when her Mac is in wireless mode. it works fine if directly connected to the router but when using WiFi some sites are available and say "can't find the server". i installed xPods and this didn't help in wireless mode but direct connection to the pod resolved this issue. Signal strenght is excellent with or without xPods.
An example is going to Apple.com. We can acccess all the drop downs ("Mac", "iPad", etc) exceplt for the "Support" as this goes to "support.apple.com" which results in "can't find server".
What is causing this inability to access all web sites while in wireless mode?
could it be possible that you are connecting to the WIFI access point of the router instead of the Xfinity device?
Maybe it is the DNS when using WIFI.
Try setting the DNS on the wifi connection to google's dns of Primary: 126.96.36.199 and Secondary: 188.8.131.52
and see what happends.
Thank you for posting to the Xfinity Forums. Have you been able to resolve this on your end? Have you tried the steps provided by @Broomsweeper to see if this helps?