Cursor is failing due to connection error

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

From past couple of day Cursor agent fails in while running a task due connection issue, but there is no issue with my connection. Due which multiple tokens are being wasted. And many times the while generating the output it abruptly terminate in between, The chat was not long and new even new chat it happens. Plus the service feel degraded if generates the any half response.

Steps to Reproduce

There are no steps chat will working and suddenly issues occurred, yesterday full day it was un workable and today as well it worked for couple of commands and then terminated with connection error.

Expected Behavior

It should generate the response and complete the task that is basic requirement. And quality of task performed should not be degraded, all these leads to lots of token wastage. All these are basic expectation.

Screenshots / Screen Recordings

Operating System

Windows 10/11

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.2.43 (user setup)
VSCode Version: 1.105.1
Commit: 32cfbe848b35d9eb320980195985450f244b3030
Date: 2025-12-19T06:06:44.644Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Windows_NT x64 10.0.26200

For AI issues: which model did you use?

Auto mode was selected with Opus 4.5 enabled

For AI issues: add Request ID with privacy disabled

Request ID: 3f22fd5b-ebbf-4762-8772-49b8292e753b

Does this stop you from using Cursor

Yes - Cursor is unusable

1 Like

Hey, thanks for the report.

This is a known network issue related to HTTP/2. Please try these steps in order:

  1. Disable HTTP/2: Settings Ctrl+, > search for “HTTP/2” > enable “Disable HTTP/2” > restart Cursor
  2. Run Network Diagnostics: Settings > Network > Run Diagnostics > send a screenshot
  3. If diagnostics don’t help, try without extensions: run cursor --disable-extensions in a terminal
  4. If you use MCP servers, disable them: Settings > Cursor > MCP

Please share:

  • A screenshot of Network Diagnostics (most important)
  • What happens when you try without extensions
  • Whether you use a VPN, proxy, or a corporate network

Related solved topics:

Let me know the results.

I had already done the network diagnostic with HTTP 2 enabled that time itself it was passing, all the test. But shouldn’t we use the HTTP 2, for optimum performance.

If you use MCP servers, disable them: Settings > Cursor > MCP - none

A screenshot of Network Diagnostics (most important) - shared

What happens when you try without extensions - there is no new extension i am using, i have basic extensions of docker, jupyter, powershell and so verified once which I have been using from very long.

Whether you use a VPN, proxy, or a corporate network - none

This is happening from past 2 days itself.

The issue still persist:

Request ID: 8c863ea6-962a-4c08-ba3c-23f04f0dbf82
ConnectError: [internal] Serialization error in aiserver.v1.StreamUnifiedChatRequestWithTools
at vscode-file://vscode-app/c:/Users/gaura/AppData/Local/Programs/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:12375:452121

Also, I have noticed another thing that it happened if the using debug mode. And when relaunch the same project as fresh chat then it was working and other project works fine but again when i started using debug it gave connection after a while @deanrie

Thanks for the important note about debug mode, that’s critical info!

This is a known issue with a serialization error related to the terminal tool. A few similar bugs have already been fixed, but your case with debug mode might be a separate issue.

Workarounds:

  1. Restart Cursor (as you noticed, this helps temporarily)
  2. Avoid debug mode when possible
  3. Start a fresh chat for new tasks

Main thread for this bug: Serialization error

Let me know what you find.

Can we just have a sustainable solution to this problem already?

2 Likes

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