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Fix 'npm run build Error Cannot Find Module' - How to Fix Cloudflare 521 Error with Firewall Settings-How to Resolve Nginx Upstream Refused Connection

2026-07-28 21:49:14developer-tools
Fix 'npm run build Error Cannot Find Module' - How to Fix Cloudflare 521 Error with Firewall Settings-How to Resolve Nginx Upstream Refused Connection

Final checklist

  • Confirm that the same symptom is gone after a restart or refresh.
  • Keep the smallest working change and undo temporary diagnostic settings.

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