Unable to access Github.com from behind Deco x60
I am unable to access github.com at all from behind the Deco x60. But if I disconnect my phone or computer from the Deco's WiFi and connect them directly to the WiFi of my Xfinity XFi modem router, then I can access github.com. The Deco is behind the XFi modem router. Both the Deco and the XFi modem operate as routers, each broadcasting its own WiFi networks. I rebooted all 3 Decos without avail.
DNS is not the problem because the github.com name resolves to the correct IP address when I am behind the Decos. Ping request to github.com times out however.
If I use VPN on my computer, then I can access github.com from behind the Deco.
On the Deco, parental control and antivirus features are all off.
I have this problem only with github.com at this point.
Please help. Thanks.