The short version

If ChatGPT works on your phone but fails on your Windows PC, and you have Intel Killer networking software installed, check:

Killer Network Service

On my machine, stopping this service restored normal HTTP/2 immediately.

The fix

Open PowerShell as Administrator:

PowerShell 
Stop-Service -Name 'Killer Network Service' -Force
Set-Service -Name 'Killer Network Service' -StartupType Disabled

Restart Windows and test ChatGPT normally.

The symptoms

  • ChatGPT took 5-6 minutes to reply or failed completely.
  • The desktop app and Codex were affected.
  • Edge and Firefox both failed.
  • The phone app worked.
  • The error was often net::ERR_HTTP2_PROTOCOL_ERROR.

How I found it

I tested browsers, accounts, internet connections, extensions, DNS and the Windows app. Nothing fixed it.

The first breakthrough was forcing HTTP/1.1. ChatGPT immediately worked when HTTP/2 was disabled:

--disable-http2 --disable-quic

That meant something on the computer was breaking HTTP/2 traffic.

The investigation

The laptop had:

Killer Wi-Fi 6E AX1675i
Killer E3100G Ethernet Controller

I checked the Killer services:

KAPSService
Killer Analytics Service
Killer Network Service
KNDBWM

Stopping all Killer services restored HTTP/2. Then I restarted them one by one.

The failure returned when this service started:

Killer Network Service

Proof

Killer Network Service running:
HTTP/2 fails, ChatGPT freezes.

Killer Network Service stopped:
ChatGPT, Firefox, Edge and Codex work normally.

After the fix

  • ChatGPT web works normally.
  • Firefox and Edge work with HTTP/2.
  • The ChatGPT Windows app works.
  • Codex works again.
  • No HTTP/2 errors.

Does this apply to you?

Check this if you have:

  • Killer Ethernet or Wi-Fi hardware.
  • ChatGPT failures only on one PC.
  • Both Edge and Firefox failing.
  • ChatGPT working when HTTP/2 is disabled.

Test first. Do not disable random networking services blindly. Change one thing at a time so you know what actually fixed the problem.

Final note

For a month this looked like an OpenAI outage, an account problem, a browser bug or an internet issue.

The actual culprit was a local Windows service with the most suspicious name possible:

Killer Network Service

Before reinstalling Windows or cancelling your subscription, check what software is sitting between your computer and the internet.