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Fix Windows Defender Missing After Update - Change Windows Update Port to Fix 'Already Allocated' Error-How to Resolve Cloudflare 521 Error Post-Update

Updated 2026-06-13 14:22:40developer-tools
Fix Windows Defender Missing After Update - Change Windows Update Port to Fix 'Already Allocated' Error-How to Resolve Cloudflare 521 Error Post-Update
Before changing system settings, save your work and note the exact error text so you can compare results after each step.

Extra verification checklist

  • Restart the affected app after changing permissions or configuration files.
  • Test the same workflow in a clean browser profile or a temporary user account.
  • Compare the result on another network if the error may be connection related.

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