IPv6 broken since at least Jan 21 (IPv4 OK) - packet capture shows ND failure, request Tier-2/CMTS escalation

Thanks for the response. I am using my own purchased modem (Motorola MB8600), not an Xfinity xFi Gateway rental, so Bridge Mode does not apply.

 Troubleshooting already completed:

 1. Power-cycled modem.
 2. Restarted WAN IPv6 on router (ifdown wan6 / ifup wan6).
 3. Rebooted router.
 4. Verified issue on router and clients (not a single-device issue).
 5. Verified DNS AAAA resolution works.
 6. Verified IPv6 still fails end-to-end (gateway and internet IPv6 ping both 100% loss).
 7. Captured WAN packets during WAN6 restart.

 Key technical findings from packet capture:

 - Router receives Router Advertisements and DHCPv6 ADVERTISE/REPLY.
 - Router gets valid WAN /128 and delegated /64.
 - Router repeatedly sends Neighbor Solicitations for upstream gateway fe80::21c:73ff:fe00:99.
 - No Neighbor Advertisement for that gateway is seen in the same capture window.
 - Result: IPv6 data path fails even though control-plane traffic is present.

@user_is0zz6, Thank you for sharing the troubleshooting steps you’ve already taken and for providing those additional details. If you could send our team a direct message with your full name, the name listed on the account (if different), and the service address associated with your account, we'd be more than happy to look into this for you.

To send a Direct Message, please click on the “Direct Message” icon in the top-right corner of the screen, next to the bell icon, click the "New message" (pencil and paper) icon, then type or select "Xfinity Support". Type your message in the text area near the bottom of the window and press Enter to send your message and initiate a live session.