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Fix Cloudflare Error 521 After a Server Update - Docker Compose Environment Variable Not Set in Container: Fixes-Cloudflare Origin Certificate Error After SSL Mode Change

Updated 2026-07-28 12:03:39office-tools
Fix Cloudflare Error 521 After a Server Update - Docker Compose Environment Variable Not Set in Container: Fixes-Cloudflare Origin Certificate Error After SSL Mode Change
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.