[BUG] Claude Desktop hangs on launch with 100% CPU (React hydration error #418)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Desktop hangs immediately after launch, showing an infinite spinner. The main Electron process pins at 100% CPU and the app never becomes usable.

The web view logs show a React hydration error on every launch:

Uncaught Error: Minified React error #418; visit https://react.dev/errors/418?args[]=text&args[]= for the full message

This error puts the renderer into an infinite re-render loop, pegging the main process at 100% CPU. A sample of the process confirms the main thread is stuck in a tight V8 microtask/rendering loop.

• claude.ai works fine in a regular browser — only the desktop app is affected
• The error occurs on every launch attempt (tested 8+ times)
• The CCD version check also loops: downloads 2.1.63, initializes, then resets and falls back to 2.1.51, re-triggering the download

What Should Happen?

Claude Desktop should launch normally, render the UI, and be usable without hanging or pegging the CPU at 100%.

Error Messages/Logs

~/Library/Logs/Claude/claude.ai-web.log:
2026-03-08 10:58:10 [error] Uncaught Error: Minified React error #418; visit https://react.dev/errors/418?args[]=text&args[]= for the full message or use the non-minified dev environment for full errors and additional helpful warnings.

~/Library/Logs/Claude/main.log:
[CCD] Falling back to installed version: 2.1.51 (required: 2.1.63)
[CCD] Downloading from https://downloads.claude.ai/claude-code-releases/2.1.63/darwin-arm64/claude.zst
[CCD] Initialized with version 2.1.63
[CCDScheduledTasks] Reset
[CCD] Falling back to installed version: 2.1.51
(download/init/reset loop repeats indefinitely)

Steps to Reproduce

1. Launch Claude Desktop (v1.1.5368) on macOS 26.3 (Apple M5)
2. Observe infinite spinner — the app never finishes loading
3. Check Activity Monitor: the main Claude process is at 100% CPU
4. Check ~/Library/Logs/Claude/claude.ai-web.log — React error #418 on every launch

Attempted remediation (none resolved the issue):

• Clearing all Electron caches (Cache, GPUCache, Code Cache, Session Storage)
• Clearing web state (Local Storage, IndexedDB, WebStorage, Cookies, blob_storage)
• Resetting window-state.json
• Force killing and relaunching multiple times
• Full reinstall via brew install --cask claude --force

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Unknown — previous version worked fine

Claude Code Version

1.1.5368 (Claude Desktop) / CCD 2.1.51 (fallback from required 2.1.63)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Note: This is a Claude Desktop issue, not Claude Code CLI.

• Hardware: Apple M5, 24GB RAM
• macOS 26.3 (Build 25D125), Darwin 25.3.0
• Shell: zsh
• A sample of the hung process shows the main thread stuck in a tight V8 microtask loop (FileHandle CloseReq → InternalCallbackScope → microtask processing → JIT JS code)
• System memory was also very low (~58MB free) at time of issue, though the 100% CPU persists even after freeing memory
• Cowork scheduled tasks (todo-scanner, evening-digest) are enabled and 35 persisted sessions were loaded on startup