At least they allowlisted Cloudflare. Are you noticing anything in common when the errors happen? Is it all Paris, or a certain URL? Here’s more 521 information:
Error
Try the suggestions in this Community Tip to help you fix Error 521 : Web server is down.
Background
A 521 error happens when we are unable to make a TCP connection to your origin server. Specifically, Cloudflare tried to connect to your origin server on port 80 or 443, but received a connection refused error. This is often caused by security or firewall software and happens if the origin server has directly refused Cloudflare’s proxy request.
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Quick Fix Ideas
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