Connection Error with Agent

Support Bug Reports
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1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

So, my Cursor Agent worked fine until Tuesday, when I asked the Agent to do something, it said “Reconnection…” and showed me this output (even if I opened a new tab of Agent) :
“Connection Error
Connection failed. Please try again, or contact support if the issue persists.
Copy Request {80706fb9-…} Try Again”
Even if I reloaded the window, it didn’t work.

Steps to Reproduce

I think I just reloaded the window because one of my extensions didn’t work normally.

Expected Behavior

The Agent isn’t working anymore.

Screenshots / Screen Recordings

Screenshot 2026-05-15 122306.png
Screenshot 2026-05-15 122306.png1920×1080 243 KB

Operating System

Windows 10/11

Version Information

Version: 3.4.17 (user setup)
VSCode Version: 1.105.1
Commit: 93e603f703cd553a6bb3644711a3379bbbb31180
Date: 2026-05-13T21:39:55.724Z
Layout: editor
Build Type: Stable
Release Track: Default
Electron: 39.8.1
Chromium: 142.0.7444.265
Node.js: 22.22.1
V8: 14.2.231.22-electron.0
OS: Windows_NT x64 10.0.26200

For AI issues: which model did you use?

Auto

For AI issues: add Request ID with privacy disabled

Request ID: 80706fb9-b0b1-486c-bbaa-c2f6b05888e1
[unavailable]
IAe: [unavailable]
at Tm0 (vscode-file://vscode-app/c:/Users/ranai/AppData/Local/Programs/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:29857:25583)
at Cm0 (vscode-file://vscode-app/c:/Users/ranai/AppData/Local/Programs/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:29857:24382)
at Dm0 (vscode-file://vscode-app/c:/Users/ranai/AppData/Local/Programs/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:29858:6490)
at zCp.run (vscode-file://vscode-app/c:/Users/ranai/AppData/Local/Programs/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:29858:11286)
at async nks.runAgentLoop (vscode-file://vscode-app/c:/Users/ranai/AppData/Local/Programs/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:42202:18635)
at async nlf.streamFromAgentBackend (vscode-file://vscode-app/c:/Users/ranai/AppData/Local/Programs/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:42270:12673)
at async nlf.getAgentStreamResponse (vscode-file://vscode-app/c:/Users/ranai/AppData/Local/Programs/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:42270:19902)
at async gSt.submitChatMaybeAbortCurrent (vscode-file://vscode-app/c:/Users/ranai/AppData/Local/Programs/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:29973:17236)

Does this stop you from using Cursor

No - Cursor works, but with this issue

6

Hey, thanks for the detailed report. The stack trace and Request ID really help.

Since the request never reaches the backend and the stack points to [unavailable] from the Connect transport, this looks like an extension host init issue in that specific window. You also mentioned one extension was acting weird before the reload. This matches a pattern we’re already tracking.

Try these in order:

  1. Open the project in a new Cursor window via File > New Window, then open the folder. Often it’s only that one broken window.
  2. Fully quit Cursor via Task Manager, kill all Cursor processes, then relaunch.
  3. Run cursor --disable-extensions from a terminal and check if Agent responds. If it does, an extension is likely the cause.
  4. If you have .cursor/mcp.json, temporarily disable the MCP servers there and restart.
  5. Go to Settings > Network > Run Diagnostics, and try enabling Disable HTTP/2 in Settings by searching for HTTP/2.
  6. In Agent, start a new chat after the restart. Don’t resume an old one.

A couple questions to narrow it down:

  • In the broken window, do Terminal, Git Source Control, and other extensions work, or is everything broken at once?
  • Does opening a new window or doing a fresh Cursor restart help?

Let me know what you find, and we’ll tell if it’s just that window or something deeper.

8

Hi. Thanks for your speed answers, because I’m currently catching up a project for my thesis defense.

Just to let you know, that before you answered my bug report, I thought uninstalling and reinstalling will solve the error, but it didn’t change anything, and after, I tried to log out and log in my account, but now it just shows me “Cursor Free Plan” instead of my account.

Let me give you feedbacks for each step you suggested me to do:

  1. The error is still there.
  2. It didn’t change anything.
  3. The agent still doesn’t work
  4. There is no mcp.json on \.cursor\, and I think I am not using MCP
  5. This is the ouput of “Network Diagnostics” :
    Cursor Network Diagnostic Results

FAILED (5): HTTP/2, API, Ping, Chat, Agent

DNS: Success
Logs:
[2026-05-15T10:35:02.847Z] Host: api2.cursor.sh
[2026-05-15T10:35:02.847Z] Servers: 127.0.0.1
[2026-05-15T10:35:02.847Z] Resolved to 3.94.199.57 in 15ms
[2026-05-15T10:35:02.885Z] Resolved to 3.94.199.57 in 1ms
[2026-05-15T10:35:02.899Z] Resolved to 3.94.199.57 in 1ms
[2026-05-15T10:35:02.902Z] Resolved to 3.94.199.57 in 1ms
[2026-05-15T10:35:02.923Z] Host: api2.cursor.sh
[2026-05-15T10:35:02.923Z] Servers: system
[2026-05-15T10:35:02.923Z] Resolved to 98.80.153.164, 52.4.240.194, 13.218.9.51, 52.44.139.99, 98.94.186.232, 32.195.133.41, 52.200.208.4, 3.94.199.57 in 11ms
[2026-05-15T10:35:02.926Z] Resolved to 98.80.153.164, 52.4.240.194, 13.218.9.51, 52.44.139.99, 98.94.186.232, 32.195.133.41, 52.200.208.4, 3.94.199.57 in 0ms
[2026-05-15T10:35:02.938Z] Resolved to 98.80.153.164, 52.4.240.194, 13.218.9.51, 52.44.139.99, 98.94.186.232, 32.195.133.41, 52.200.208.4, 3.94.199.57 in 1ms
[2026-05-15T10:35:02.940Z] Resolved to 98.80.153.164, 52.4.240.194, 13.218.9.51, 52.44.139.99, 98.94.186.232, 32.195.133.41, 52.200.208.4, 3.94.199.57 in 1ms
[2026-05-15T10:35:02.940Z] Result: true

HTTP/2: Error: Unexpected protocol: undefined
Logs:
[2026-05-15T10:35:02.810Z] Start
[2026-05-15T10:35:04.924Z] Host: api2.cursor.sh
[2026-05-15T10:35:04.924Z] Protocol: undefined
[2026-05-15T10:35:04.924Z] Result: Error: Unexpected protocol: undefined in 2114ms

SSL: Running
Logs:
[2026-05-15T10:35:02.810Z] Start
[2026-05-15T10:35:04.928Z] URL: undefined
[2026-05-15T10:35:04.928Z] Status: undefined
[2026-05-15T10:35:04.928Z] IP: undefined
[2026-05-15T10:35:04.929Z] Issuer: undefined
[2026-05-15T10:35:04.929Z] Name: undefined
[2026-05-15T10:35:04.929Z] AltName: undefined
[2026-05-15T10:35:04.929Z] DNS Time: undefinedms
[2026-05-15T10:35:04.929Z] Connect Time: undefinedms
[2026-05-15T10:35:04.929Z] TLS Time: undefinedms

API: Error: [unavailable]
Logs:
[2026-05-15T10:35:02.816Z] Start
[2026-05-15T10:35:03.677Z] Error: ConnectError: [unavailable]

Ping: Error: [unavailable]
Logs:
[2026-05-15T10:35:02.817Z] Sending ping 1
[2026-05-15T10:35:03.678Z] Error: ConnectError: [unavailable]

Chat: Error: [unavailable]
Logs:
[2026-05-15T10:35:02.818Z] Starting stream
[2026-05-15T10:35:03.679Z] Error: ConnectError: [unavailable]

Agent: Error: [unavailable]
Logs:
[2026-05-15T10:35:02.821Z] Starting stream
[2026-05-15T10:35:02.822Z] Pushing first message
[2026-05-15T10:35:03.680Z] Error: ConnectError: [unavailable]

Marketplace: Success
Logs:
[2026-05-15T10:35:02.799Z] Host: marketplace.cursorapi.com
[2026-05-15T10:35:03.149Z] Response in 350ms
[2026-05-15T10:35:03.149Z] Response: 200
[2026-05-15T10:35:03.149Z] Response Type: cors
[2026-05-15T10:35:03.149Z] Server: null
[2026-05-15T10:35:03.149Z] Result: OK in 350ms

Authentication: Success
Logs:
[2026-05-15T10:35:02.802Z] Host: prod.authentication.cursor.sh
[2026-05-15T10:35:04.150Z] Response: 200 in 1348ms

Authentication UI: Success
Logs:
[2026-05-15T10:35:02.810Z] DNS lookup: authenticator.cursor.sh
[2026-05-15T10:35:02.883Z] Resolved authenticator.cursor.sh to 172.64.152.23 in 58ms

Cursor Tab: Success
Logs:
[2026-05-15T10:35:02.811Z] DNS lookup: api3.cursor.sh
[2026-05-15T10:35:02.884Z] Resolved api3.cursor.sh to 104.18.19.125 in 58ms

Agent Endpoint: Success
Logs:
[2026-05-15T10:35:02.811Z] DNS lookup: agent.api5.cursor.sh
[2026-05-15T10:35:03.465Z] Resolved agent.api5.cursor.sh to 54.163.65.150 in 638ms

Codebase Indexing: Success
Logs:
[2026-05-15T10:35:02.811Z] DNS lookup: repo42.cursor.sh
[2026-05-15T10:35:02.885Z] Resolved repo42.cursor.sh to 52.21.111.239 in 58ms

Downloads: Success
Logs:
[2026-05-15T10:35:02.808Z] Host: downloads.cursor.com
[2026-05-15T10:35:03.729Z] Response: 403 in 921ms

CDN: Success
Logs:
[2026-05-15T10:35:02.809Z] Host: cursor-cdn.com
[2026-05-15T10:35:03.599Z] Response: 404 in 790ms

  1. I’ve already tried that before, but it still didn’t work.

Yeah, the Terminal and the other extensions still work normally, and no, opening a new window or doing a fresh Cursor restart didn’t help.

I hope you really could help me as quick as possible please, because as I said I’m catching up my project for my thesis defense, because Cursor can do the coding while I’m focusing on thinking about the project architecture and features.

Thank you again for your help.

9

Thanks for the detailed feedback. Network diagnostics cleared up a lot, and this is not the same issue I first suspected.

Here’s what I’m seeing. DNS works. Authentication, Marketplace, agent.api5.cursor.sh, api3.cursor.sh, Downloads, and the CDN all return 200 OK. But api2.cursor.sh specifically, the API used for Ping and Chat, fails with ConnectError: [unavailable] in about 860 ms, and the HTTP/2 negotiation returns Unexpected protocol: undefined. That also explains why after re-login you see Cursor Free Plan, because the subscription check goes through api2.cursor.sh too.

This means something on your machine or network is specifically blocking traffic to api2.cursor.sh, or blocking HTTP/2 to it. Reinstalling, extensions, or MCP won’t help since this is a lower-level network issue.

What to check, in order, with the quick tests first:

  1. Mobile hotspot test, most important. Connect your laptop to your phone’s mobile internet and try Agent. If it works, the issue is your network, router, or ISP. If it doesn’t work, the issue is on the machine, like AV, firewall, or VPN.

  2. VPN or proxy. If you have a VPN enabled, Zscaler, Cloudflare WARP, or any corporate proxy, fully disable it and restart Cursor. SSL inspection often breaks HTTP/2 for specific hosts.

  3. Antivirus or Windows Defender Firewall. Temporarily disable any third-party antivirus if you have one. Also check Windows Defender Firewall, add Cursor to exceptions, or temporarily turn the firewall off to rule it out.

  4. Local DNS proxy. Diagnostics show one DNS server is 127.0.0.1, so you have a local DNS resolver or blocker installed. For example pi-hole, AdGuard Home, NextDNS, dnscrypt-proxy. Check if it’s blocking api2.cursor.sh. Temporarily disable it and use system DNS.

  5. PowerShell test. Run this in PowerShell:

    Test-NetConnection api2.cursor.sh -Port 443
curl.exe -v https://api2.cursor.sh/

    Share the output. This will clearly show if TCP even reaches the server.

Given your security setup, the fastest path is step 1 with the mobile hotspot. If everything works there, you can keep coding on it for now while you troubleshoot the home network.

Let me know what the hotspot test shows and what VPN or AV you have installed.

10

Hi again.

Just want to tell you thank you for taking time to help me. I just changed my connection (I think it didn’t work because I was connected to the network at my workplace that is ruled my PfSense) by using my connection at home (I couldn’t try it yesterday because we weren’t home).

Have a nice day.