ERR_CONNECTION_TIMED_OUT on WordPress
Why it happens on WordPress
A PHP worker pool exhausted by a slow plugin or a runaway cron job accepts no new connections, so the site times out while the server itself is fine.
The fix on WordPress
Disable wp-cron's default request-driven mode and run it from system cron, then check PHP-FPM's pm.max_children against actual usage. Deactivate recently added plugins one at a time to find the blocker.
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
WordPress 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