Claude Desktop/Web: Severe UI performance regression due to infinite React render loop in skills system #4896

Problem Summary

Claude Desktop and Claude Web become unusable after 4-5 messages in a conversation due to severe UI lag (1-2 second input delay, scroll stuttering). Multiple users report this issue started around July 30, 2025.

Technical Root Cause

Infinite React render loop triggered by failing API call to skills system:

GET /mnt/skills/all_skills.json → 404 Not Found
→ useEffect() triggers retry → component re-renders → new GET → still 404
→ loop repeats endlessly (1000+ times per session)

Impact

• Input lag: 500-2000ms delay before letters appear
• UI performance: Scroll and interaction stutter
• Memory growth: Constant heap inflation
• Cross-platform: Affects both Claude Desktop (Electron) and Claude Web (Chrome/Firefox)

User Reports

Multiple users experiencing identical behavior across platforms:

• System: Windows 11 Pro 24H2, 12-core CPU, 64GB RAM, NVMe SSD
• System usage: <10% during lag
• Claude Desktop version: v0.12.55 (d55c63) - build 2025-07-25T17:43:32.000Z
• Key finding: Same lag occurs in Claude Web when opening identical chats
• Confirmation: Second user reports conversations become "basically unusable" after certain length

Technical Analysis

Error patterns observed:

• Sentry flood (429 Too Many Requests)
• Auth warnings (FedCM get() rejects, Cross-Origin-Opener-Policy issues)
• Repeated stack traces:

ux @ ...js:1
uS @ ...js:1

Cross-platform consistency:
Claude Desktop is an Electron application that loads claude.ai in a Chromium container. Both Claude Desktop and web browsers use the same Chromium rendering engine, confirming this is a frontend React issue affecting the shared codebase, not a local system problem.

Timeline Correlation

Issue appeared around July 30, 2025, coinciding with Anthropic's reported incident:

Claude.ai chats appearing out of chronological order
Resolved - Jul 30, 21:23 UTC
Investigating - Jul 30, 03:07 UTC
"We are currently investigating an issue causing some past chats to appear to have been recently updated. As a result, the chronological order of your past Claude.ai chats, including the recent chats view, may be incorrect."

This suggests the performance regression may be related to the chat ordering infrastructure changes.

Recommended Fix

Immediate:

• Temporarily disable skills system until proper error handling implemented

Long-term:

• Add retry limit or circuit breaker in useEffect for skills API calls
• Implement graceful failure instead of re-render looping
• Add proper error boundaries around skills components

Environment

• OS: Windows 11 Pro 24H2
• Claude Desktop: v0.12.55 (d55c63) - Electron/Chromium-based
• Browser: Chrome v138.0.7204.183, Firefox (same behavior)
• Timeline: Issue started around July 30, 2025

Reproduction Steps

1. Start new conversation in Claude Desktop or Web
2. Exchange 4-5 messages
3. Observe increasing input lag and UI stuttering
4. Check browser dev tools for repeated 404 errors on skills endpoint

This appears to be a critical performance regression affecting multiple users across platforms due to shared Chromium/React frontend architecture.