IPv6 prefix delegation failing "No prefix available on Link"

Beginning sometime yesterday (16 Jun 2015) afternoon, I no longer received an IPv6 prefix delegation from comcast:

Jun 17 12:18:05.357 PDT: IPv6 DHCP: Received ADVERTISE from FE80::21D:70FF:FECC:58E2 on FastEthernet0
Jun 17 12:18:05.357 PDT: IPv6 DHCP: detailed packet contents
Jun 17 12:18:05.357 PDT: src FE80::21D:70FF:FECC:58E2 (FastEthernet0)
Jun 17 12:18:05.357 PDT: dst FE80::216:C7FF:FE7C:BFBC (FastEthernet0)
Jun 17 12:18:05.357 PDT: type ADVERTISE(2), xid 12121931
Jun 17 12:18:05.357 PDT: option CLIENTID(1), len 10
Jun 17 12:18:05.357 PDT: 000300010014A412E3B0
Jun 17 12:18:05.357 PDT: option SERVERID(2), len 14
Jun 17 12:18:05.357 PDT: 0001000117323D5614FEB5D6E776
Jun 17 12:18:05.357 PDT: option IA-PD(25), len 71
Jun 17 12:18:05.357 PDT: IAID 0x00020001, T1 0, T2 0
Jun 17 12:18:05.357 PDT: option STATUS-CODE(13), len 55
Jun 17 12:18:05.357 PDT: status code NOPREFIX-AVAIL(6)
Jun 17 12:18:05.357 PDT: status message: No prefix available on Link 'wa-everett-ten05-link-S'
Jun 17 12:18:05.357 PDT: option PREFERENCE(7), len 1
Jun 17 12:18:05.357 PDT: preference value 0
Jun 17 12:18:05.357 PDT: option DNS-SERVERS(23), len 32
Jun 17 12:18:05.357 PDT: 2001:558:FEED::1
Jun 17 12:18:05.357 PDT: 2001:558:FEED::2

I am using a Motorola SB6121 modem and a Cisco router, and this was functional until yesterday.  Comcast T2 support told me only that because I own my own modem, they cannot investigate.  I'm skeptical that this is due to my modem or router, as it worked correctly until yesterday, receiving a /56 delegation, and my router still receives a unicast /128 IPv6 address that functions correctly.

There is another report on the xfinity forum with the same issue

http://forums.xfinity.com/t5/Home-Networking-Router-WiFi/IPv6-prefix-delegation-after-months-of-working-fine-today-no/m-p/2543256#M91305

I have replied there as well.

Is anyone else experiencing this problem?