IPv6 has stopped working for me on comcast as well with .41. it seems dhcp6 isn't assigning addressed anymore
And yet there are other Comcast customers who have no issue with IPv6, so it seems to vary from node to node.
At this point I've reached the conclusion that Comcast's IPv6 implementation is simply broken. In the past two years they are the ISP that generated the highest number of issues with Asuswrt and IPv6.