Solved! Go to Solution.
For anyone else with similar issue, at long last this was resolved. I kept striking out with Level 2 techs on both the Comcast and Arris sides and ComcastPhil was exteremly helpful but ultimately could not identify a problem on his end. Finally someone up the escalation chain on Arris’s side reached out to an acquaintance tech at Comcast and between them, they were able to perform some sort of reactivation that fixed the IPv4 connectivity. I have no idea what they did and unfortunately the tech that informed me of the fix having been performed was just the messenger and unable to explain it either. It sounded like something in the Comcast backend that had to be fixed manually given how many times I attempted hard reset and/or had the device reactivated to fix the issue with no luck.
Best of luck to anyone else with this issue. FWIW, it seemed to be a problem unique to this one single modem. If this ever happened again I’d probably recommend cutting losses and replacing the modem with a new or different one. This was quite a month-long headache. Thanks everyone for the help.