2000/250 Mbps plan stuck at ~60 Mbps upload — no OFDMA channel provisioned on XB8

I am using the post made by user_3b0d4g (https://forums.xfinity.com/users/6a9b8fe08e6b2f40dc997b4c) (https://forums.xfinity.com/conversations/your-home-network/2000250-mbps-plan-stuck-at-80-mbps-upload-no-ofdma-channel-provisioned-on-xb8/6a9b93fecd56d5a37c7b984d) one month ago for the base wording of this question. Their problem is exactly my problem with slightly different numbers, and clearly I'm less patient than they are.

I'm on the 2000 Mbps download / 250 Mbps upload plan using the free Xfinity XB8 gateway (Technicolor CGM4981COM). Download speeds exceed expectations (generally above 2000 Mbps), but upload is consistently capped around 60 Mbps — nowhere near the 250 Mbps I'm paying for.

What I've found after checking the gateway's own connection status page:

- Upstream: 4 bonded channels, all using ATDMA/QAM modulation at the following frequencies; 16, 22, 29, & 35 MHz. All 4 are locked with clean power levels, but there is NO OFDMA upstream channel present at all. 

- Transmit power is showing 38.3, 39.0, 39.8, and 40.3 dBmV

This looks like a mid-split/Next Gen upload provisioning issue — my account or gateway doesn't appear to have been switched over to the OFDMA upstream service profile, even though the XB8 fully supports it and my address was confirmed months ago when I agreed to switch over to the 2G plan. 

What I've already tried, all without resolution and not necessarily in the right order:
- Replaced my owned Arris G54 modem with an Xfinity modem - same Upload slowness
- Xfinity chat support - pleasant technician following a list of steps. They did themselves credit putting up with me. 
- Had an on-site service technician visit and physically test all wiring from street to endpoints in the house. 

Every one of these gave me the same generic WiFi/signal troubleshooting steps (router resets, reseating cables, etc.). None of them checked or mentioned OFDMA provisioning or the upstream service profile on my account, which based on my own diagnostics looks like the actual root cause. 

I'd like this escalated to Advanced Repair or Network Provisioning/Engineering specifically to check:
1. Whether my account is provisioned for the mid-split/Next Gen upload tier
2. Whether the correct bootfile/service flow has been pushed to my gateway's MAC address to activate the OFDMA upstream channel

Happy to provide my full name, service address, and gateway MAC address via direct message. Thanks for taking a look.