IPv6 Problems

I've had IPv6 working for over a year, but I've recently started having issues getting IPv6 connectivity.  Location is Portland, OR.

Setup:  Hitron CODA56 Modem ---> pfSense ---> LAN

I see a normal-looking DHCP6 transaction, and get assigned an address for the firewall as well as a /64 delegated prefix.  Then I can monitor the pfSense WAN interface and see IPv6 traffic going out, but no replies to any outgoing packets, not IP6 or ICMP6.  Nothing.

I have already tried power-cycling the modem followed by rebooting the pfSense firewall.  The DHCP6 transaction looks completely normal but it appears Comcast isn't routing my IPv6 traffic at all.

How do I troubleshoot this?

Google Drive link to pcap file showing DHCP transactions (4 and 6): [Edited: "unknown link"]