Very strange.
Can NOT log laptops, ipad or either phone into internet. connects to router but will not get an internet connection. TVs are running fine on Roku connected to router/modem.
All my ring cameras are running fine connected to router/modem.
All connected devices show in router admin Client List but no internet on phones iPad or laptops the rest work fine
Laptop via Ethernet cable to modem no internet....
Logged my phone into other Wi-Fi at different locations with no issues.
Asus RT-N66U router firmware version 3.0.0.4.378_9459
SURFboard SB6141 modem ipv6 only
Xfinity ISP provider