Another broken dhcpv6-pd complaint on brand new DPC3939B

Thanks so much for taking the time to reach out to us through our business forums. I very much appreciate your patience and greatly apologize for the delay in our response. I know how important the services are to your business and we want to do all that we can to assist. I know how impactful any service issue is to your business as I use my connection daily for business purposes. I would love to get to the bottom of the IPV6 issues and help you get back to business as usual. Can you please reach out through private message with your first and last name, business service address and account number or phone number? 

Thank you for your patience and for sending us that private message! We will continue in assisting you from there.

The best I managed so far was to set up a script to automatically reboot the modem every day.  That sort of works except that the network is offline for the ten minutes it takes to reboot and sometimes the modem doesn't actually come back up on its own.

Go figure, Comcast went and locked my thread prior to achieving any resolution.  That's not how community forums are supposed to work!  *sigh*

At this point I will likely be switching to bridge mode until this can be remedied, I need some kind of native IPv6 more than I need static IPv4. I'll have to work around whatever limits I have there, and do without the externally available stuff I had prior - maybe move it to ZeroTier or something.

I am out of contract and JUST requested a new one be generated. I will not be signing until I have a positive resolution on this issue. 

I can truly understand how important this service is to your business and we are going to work to ensure that we get this resolved for you. I appreciate your patience and all the time you are delgating out of your day to assist us with this. I will continue to reach out through our private message with you so we can continue to work to get this resolved. 

I moved some of my stuff to Hurricane Electric for IPv6... its not as fast (extra hops) but it works and it is static.

That's a bummer.  Unfortunately it doesn't seem like the Tier 2 support people talk much to each other.  So even though we're all having the same problems with IPv6 routing and prefix delegation, they aren't comparing notes on the back-end or testing their hypotheses before applying changes to consumer equipment.

For example, the support team just downgraded my gateway's firmware and it broke IPv6 routing completely.  I have to assume that the same thing would have happened in the lab had anyone tried it.

I would really like to close the loop with a programmer on the software team who has direct insight into the modem's internal operation and who is able to be more methodical about reproducing and debugging these common issues.

I truly apologize that this has been your experience. I am going to set up a follow up for tomorrow morning as our Advance Repair Team should be in the office and available for an update. I can't thank you enough for your patience and willingness to work with us. I know that certain conditions may take more time resolve. However, we will continue to own this issue and work together to get to the bottom of this. 

The saga continues, I ended up doing a whole bunch of stuff. 
I was told in no uncertain terms that the modem they replaced my old one with will never do v6 correctly, I won't say how or from who, but I trust this source. So, I canceled my static IPs, replaced my cable modem with the one I bought (an Arris SB8200). That broke v6 in so much that it only seems to support one /64, which is functionally useless to me. I did almost no troubleshooting and can’t find any docs on it, it doesn’t seem to be configurable that I can find. Calling comcast yielded no useful results as they "can't see into that modem in bridge mode", so they can't help. OK, fine. It's not worth the time to argue, and since there are zero configuration options on that modem that I can find, I'll switch back. 
I switched back to the comcast modem. That took about 2 hours last night to get them to at least pretend to understand what I was talking about. Re-provisioning the old modem got me v4 again. v6 takes forever to provision, for whatever reason, but does eventually finish after about 20 minutes. This device also has some serious stability issues in that I have to hard reset it about every 5 days, which is not acceptable for what I pay for this service.

Going back through my notes from 5+ years ago, I found that when you request a static IP a level2 tech has to call you, so, I called and had them re-add a single static ipv4 address, which they called me to provision the next day around 8am. Once I had that, I set it back to bridge mode and I am back to dynamic everything working. At this point v6 is still broken, so I told the level2 tech my issue and he offered to replace the puma based modem with a CGA4131COM. What do I have to lose at this point?

IPv6, apparently. 

This modem delegated me a /59 once, which didn't work and seems broken in the same way as the last modem, but at least doesn't have the same stability issues as the last device.  At this point I am now 100% without IPv6 connectivity. Even in bridge mode the behavior is totally broken, I get no ipv6, period. Part of the issue appears to be that the WAN Default Gateway Address (IPv6): within the comcast modem seems to take forever to populate (typically done via a RA). 

Come on, this is almost comically bad at this point. Maybe we should do a youtube "historical fiction" comedy about this process. Youtube is totally dial stacked, we could stream it totally over v6....unless, of course, you have comcast business service. 

This seems like a problem. The blacked out areas all look normal and correct. This is on a CGA4131COM that was installed this morning. The lack of a v6 next-hop is pretty telling as to why nothing works. 

Hello, I just wanted to take some time and reach out to you and check in. Has there been any change with the IPV6 routing issue? Have you heard from our advanced repair teams at all? 

Thanks so much for taking the time to reach out to us through our business forums. I very much appreciate your patience and greatly apologize for the delay in our response. I know how important the services are to your business and we want to do all that we can to assist. I rely on my connection daily and I can understand how frustrating it is that the services are not meeting your expectations. I would love to assist with the IPV6 issues that you are experiencing and get you back into working abilities. Can you please reach out through private message with your first and last name, business service address and account number or phone number?