Windows Security App Not Opening? Try These Steps - Fix Cloudflare 521 Error by Adjusting Firewall-Troubleshooting Nginx Upstream Connection Refused 443
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.