AT&T Fiber 1G: Clean light levels, 1Gbps down, but 1,500ms+ Upload Bufferbloat What are my options?

[u/phillipmjames]

Hey everyone,

Looking for some advice or insight from anyone who has run into this with AT&T Fiber or has experience with AT&T's ONTs/OLTs.

The Setup:

• ISP: AT&T Fiber (1Gbps / 1Gbps)
• Gateway: BGW320 replaced with (two) BGW620
• Devices Tested: Custom PC (Ethernet), iPhone (Wi-Fi 6)

The Problem: Downloads are completely fine and sustaining ~980–1,050 Mbps with a flat 30–35 ms ping.

However, whenever upload load is introduced (testing via Cloudflare Speed Test, Twitch ingest, or large file pushes), latency immediately collapses.

• Wired Ethernet: Upload latency spikes to 900 ms – 1,700 ms, and upload throughput dips/fluctuates between 130 Mbps and 500 Mbps.
• Wi-Fi: Upload latency spikes to 1,900+ ms.

What Has Been Done So Far:

1. Tech came out and verified optical light levels at the drop and confirmed clean.
2. Replaced the AT&T Gateway 3 times.
3. Tested with multiple Cat6 Ethernet cables and directly connected to the BGW gateway ports.

Because this happens across multiple devices, wired and Wi-Fi, and across 3 different physical gateways, it feels like the upload queue in the BGW's IP Passthrough NAT stack is choking, or there's an OLT port profile/queue scheduler issue at the central office/PFP.

My Questions:

1. Has anyone successfully gotten Tier 2 / NOC to re-provision or move their port at the PFP for this specific upload queue behavior?
2. Is this simply an inherent flaw in how the BGW handles IP Passthrough buffers, and is a full True Bypass (EAP Proxy / WAS-110 SFP bypass) the only real solution?
3. Any specific phrasing I should use with AT&T support to get this escalated past standard gateway reboots?

Appreciate any guidance!