ERR_CONNECTION_TIMED_OUT on Cloudflare
Why it happens on Cloudflare
When Cloudflare cannot reach the origin it returns error 522 rather than passing the timeout through, so a browser timeout with Cloudflare in front usually means the edge itself is unreachable.
The fix on Cloudflare
Compare the origin directly by IP against the proxied hostname. If the origin answers and Cloudflare does not, check that the origin firewall allows Cloudflare's IP ranges rather than only your own.
Is ERR_CONNECTION_TIMED_OUT happening on your domain?
An uptime probe from outside your network tells you whether the server is unreachable for everyone or only from where you are sitting — which is the first fork in every timeout diagnosis.
Free, no signup. Runs from outside your network, which is the only way to tell a server fault from a local one.
If that didn't fix it
Cloudflare has its own failure mode, but ERR_CONNECTION_TIMED_OUT has a wider set of causes that apply everywhere. The most common one overall is: the origin server is down or the web server process has stopped.
All causes and fixes for ERR_CONNECTION_TIMED_OUT