Arris S34, OFDMA upstream channel not provisioning for next-gen upload

It seems my new Arris S34 isn't being being provisioned with the latest firmware and/or boot file needed to take advantage of the OFDMA upstream bonded channel necessary for next-gen upload speeds. This is a problem related to slow S34 upload speeds that I'm seeing in the forums here and elsewhere. My experience lines up with the others.

I upgraded from an S33 to an S34 after upgrading my service tier from Gigabit+ to GigabitX2 (2000/300 speeds) earlier this week.

My current Arris S34 firmware version is AT01.01.010.042324_S3.04.735

I'm testing speeds using a wired network that's 2.5gbps from the modem to a 2.5gbps firewall (OPNsense), to a 2.5gbps managed switch, to a 2.5gbps integrated NIC on my motherboard.

Speed tests from several services show I'm downloading at up to 2030mbps, but my uploads never go higher than 85mbps. I'll see an initial burst to around 85mbps but then is settles to 70-80mbps.

When booting my modem and signing into its web GUI as soon as it's available, I briefly see what should be the OFDMA channel appear with the status "Unlocked" (instead of "Locked") and channel type "Unknown" (instead of OFDMA). While is says "Unknown", it does show the expected OFDMA frequency of 36200000 Hz and width of 44400000.

After a moment of the modem being back online (web browsing working on devices), the "Unknown" channel disappears suggesting it was unable to be established with Xfinity.

I've worked my way through web chat support, tier 1 phone support, and then a supervisor. All were very kind and helpful but unable to resolve the issue. If there's someone from higher levels of Xfinity tech support or engineering familiar with this issue that can resolve this, I'd be grateful for your help.

Here's one helpful related post for reference:

https://www.reddit.com/r/Comcast_Xfinity/comments/1fkay76/arris_s34_is_finally_working_for_nextgen_fast/

tl;dr: "It seems I was not getting the correct boot file when my modem restarted, but a "special code" can help force the right boot file to be sent. Here is a quote from the support rep: "I have a code that I can add to try and force the correct bootfile to come through. We add that in our billing system but it doesn't change any details of your plan or pricing. This will cause the modem to provision again and reset. This should get the faster speed coming through when you are back online.""

After this, the forum user's uploads were performing at next-gen speeds. They also reported having disconnected their firewall/router from the modem to avoid any conflicts during provisioning but weren't sure if it had any impact. I've tried disconnecting my firewall alongside a regular reboot, but not coordinated with Xfinity pushing a reboot / re-provisioning the modem.