If you have a router that is no longer getting #IPv6 via DHCPv6-PD on Comcast Xfinity, check to make sure your firewall rules only require that ports 546 and 547 UDP have one of the source or destination be in fe80::/10. Comcast seems to be sometimes sourcing their DHCPv6 from 2001:558::/32 IPs rather than link-local, and some routers seem to deny in this case.

It sounds like Comcast just made this change in some markets and break some MikroTik and OpenWRT which assume a source in fe80::/10.