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How to Fix Cloudflare 521 Error with Firewall Settings - Troubleshoot ERR_CONNECTION_RESET in Chrome with VPN-Fix Nginx Configuration Test Failure from Rewrite Rules

Updated 2026-07-28 10:02:34browser-issues
How to Fix Cloudflare 521 Error with Firewall Settings - Troubleshoot ERR_CONNECTION_RESET in Chrome with VPN-Fix Nginx Configuration Test Failure from Rewrite Rules
Likely symptom
Likely cause
Safe rollback

Verification route

  • Repeat the original action, not only a simplified test case.
  • Restart the app or reload the service after configuration changes.

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