I seem to be having a similar problem as many before you related to having limited access to only major IPv6 sites. In my case, it seems to be intermittent issues. Sometimes, no access. Sometimes, limited to IPv6, sometimes limited to IPv6 on specific devices. As a property manager, I've encountered a large amount and variety of devices. On some devices (sometimes the entire network of devices at specific moments in time), all internet access is lost to non IPv6 addresses. There are also moments in time where there is no internet usage for weeks/months at a time (as there are no short term rental/property owners present and the issue does not become immediately recognizable). Perhaps this is a similar issue, as rebooting/hard resetting the router tends to fix the problem for some interval of time. The router model is a TG3482G.
Additionally, after speaking with comcast support and requesting an administrative admin/pass reset for the router itself, I was told that it was already reset to it's defaults (10.0.0.1 gateway after connecting to the associated SSID). So I've used the default configuration "admin","password" (without quotes) but have yet to receive any luck. Another technician is to be arriving tomorrow between 5-9pm but I'm concerned that he won't be able to tell me anything that I don't already know about the current configuration ( Previously an IT Administrator, now Software Developer - managing the property for some family members ). Before I leave, I will be copying down all of the hardware information and hope to hear a reply from you as I've seen you've been able to help many others as I don't even live in the same state as the property.
Any help would be greatly appreciated!
Thank you for your time,
OceanviewKiawah, thanks for posting about your iPV6 issues on your TG3482G modem. A hard Factory reset is needed to restore the modem's login in for (admin, password). Do you know if that was done specifically? It can also be done via the reset button on the physical modem itself. Do you know if those iPV6 addresses were via secured websites (https://)?