Hello,
Time by time i am getting error 521 for random css and js files.
For instance https://example.com/assets/main.css
may lead to error 521 but https://example.com/assets/main.css?2
loads just fine.
All seems to work fine after switching on the development mode from cloudflare->catching.
I am using plesk Obsidian on AWS server, and my domain has letsencrypt ssl certificate.
I run this issue with plesk support and they confirmed that there are no local issues on the server.
I really hope that somebody from here will be able to help.