Claude Code 2.1.143 silently hangs MCP tool calls after SSE drop — client logs the drop but does not fail or reconnect

What this error means

SSE connection dropped after N seconds uptime; Tool 'X' still running (30s elapsed) ... [onCancel] source=local; McpError: MCP error -32001: user-cancel is a Claude Code failure pattern reported for developers trying to fix claude code mcp tool call hanging indefinitely after server-side sse stream drops due to network timeouts or container restarts. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue #60061 opened May 18 2026 by arbitermano with verbatim debug logs showing SSE drop detection but zero reconnect attempt. Affects any deployment using SSE-transport MCP servers behind reverse proxies. P0 priority — broken AI coding workflow blocking production sessions.

Common causes

• GitHub issue #60061 opened May 18 2026 by arbitermano with verbatim debug logs showing SSE drop detection but zero reconnect attempt. Affects any deployment using SSE-transport MCP servers behind reverse proxies. P0 priority — broken AI coding workflow blocking production sessions.

Quick fixes

1. Confirm the exact error signature matches SSE connection dropped after N seconds uptime; Tool 'X' still running (30s elapsed) ... [onCancel] source=local; McpError: MCP error -32001: user-cancel.
2. Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
3. Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/anthropics/claude-code/issues/60061

Evidence note: GitHub issue #60061 opened May 18 2026 by arbitermano with verbatim debug logs showing SSE drop detection but zero reconnect attempt. Affects any deployment using SSE-transport MCP servers behind reverse proxies. P0 priority — broken AI coding workflow blocking production sessions.

Related errors

• AI Coding Tools

FAQ

What should I check first?

Start with the exact SSE connection dropped after N seconds uptime; Tool 'X' still running (30s elapsed) ... [onCancel] source=local; McpError: MCP error -32001: user-cancel text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Claude Code workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without SSE connection dropped after N seconds uptime; Tool 'X' still running (30s elapsed) ... [onCancel] source=local; McpError: MCP error -32001: user-cancel.