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

I need Tier-2/CMTS engineering review for a persistent IPv6 outage.

Summary:
- IPv4 works normally.
- IPv6 has been broken since at least Jan 21, 2026 (previous router reboot).
- This is reproducible on both router and LAN clients.

Technical evidence (already captured):
1) Router receives IPv6 control-plane:
- DHCPv6 SOLICIT/ADVERTISE/REQUEST/REPLY seen on WAN
- IA_NA + IA_PD delivered

2) Router receives Router Advertisements from upstream gateway.

3) Data-plane/ND failure:
- Repeated Neighbor Solicitations for the advertised upstream gateway
- No Neighbor Advertisement observed for that gateway in packet captures
- ping6 to upstream gateway = 100% loss
- ping6 to external IPv6 targets = 100% loss

4) Reboots and resets already attempted:
- Modem power-cycle
- wan6 ifdown/ifup
- Full router reboot
- No recovery

Request:
Please escalate to Tier-2/CMTS engineering and review IPv6 ND/forwarding behavior for my session. I can provide full report + pcap files privately.

Please DM with:
1) case/ticket number
2) escalation queue/team name
3) ETA for engineering update