XB7-T Bridge Mode Resets to Router and 2.5Gbps port stops working

Thanks for the response, and like many, I especially hate when people don't circle back to the solution when it is found. In my case, I took a trip up to the Xfinity store and within 10 minutes was headed back home with the XB8 modem. It was a bit more bulky than the prior model, but the software experience was near identical. Perhaps the main difference is that it actually worked when setting it up, as the the old model XB7-T would fail to reset to factory setting consistently, disallow the mandatory password change after the reset and then just forget when I did reset the password. Anyway, I setup the XB8, activated it with Xfinity via the app and then immediately put it into BRIDGE mode to connect to my UDM DR SE - which appeared to work fully - including the 2.5 gigabit link. I did have one minor hiccup along the way, as the modem would only operate at base speed (600Mbps and 10Mbps upload -which is a far cry from the 1.2Gb / 250Mb speeds I was paying for. It took me talking to Xfinity to get the modem 'enabled/activated' correctly on my billing account (which begs the question, what was the point of me activating it?). Unfortunately, whatever reset/update Xfinity did on their end caused the modem to, yes you guessed it, reset back to router mode and out of bridge mode. Fortunately, since that reset, and me subsequently reverting it AGAIN back to bridge mode it has now stayed in bridge mode. I am at 30+ hours of it staying in bridge mode thus far. If it reverts again back to router and out of bridge mode I will be forever done with Xfinity supplied modems.  As a backup, I have my own D3.1 capable modem, new in box, waiting to either sub OR be returned to the shop in a weeks time depending on how things go.

We are glad to hear that the Xb8 is working better for you so far, riboflavins . The behaviors reported are certainly ones that we can look into for a possible patch down the line. The XB8 disabling bridge modem during provisioning is a formal part of that process, as settings are put to default.  

@riboflavins​ Have you experienced any speed loss using the XB8 in Bridge mode or any other issues? When using Bridge mode, do you still get firmware updates from Xfinty? Last question, lol... does this affect your account at all? Meaning, your monthly data limit or do you retain unlimited data?

@YoSoyElJeffie​ In the end, no speed loss. If anything, and this is anecdotal only, my down and upload speeds appear to be a little faster with the XB8 versus when I occasionally got XB7-T working in bridge mode. When I say a little, I am talking at most an extra 100Mbps down and 50Mbps up.  I don't know if I still get firmware updates or not, but from comcast's side, the modem looks the same to them. It is in sync with their servers and has a WAN address. I would prefer they not push anything down to my modem (or reset it for that matter) when it is otherwise already working fine. So unless there was an admin menu I missed before I switched to bridge mode, I did not see any ways to control the firmware version.  When in bridge mode, Comcast still definitely tracks data consumption. I am on an unlimited plan so I don't worry about that too much anyways. I do know, however, when I did use my own cable modem they did not know what my data consumption was - at least the rep indicated the apps they use isn't showing it as he wanted to tell me how much data I used while upselling me to unlimited. I asked for unlimited to start with, so not sure why they can't take yes for an answer. I suspect this is why comcast is essentially paying customers to use their equipment. In my case, I save 5 dollars a month by using their modem/gateway over my own. This is the only reason I fought with this otherwise overly complicated and unreliable hardware in the first place!