Typically these are either client-side problems (issues with your network connection or firewall) or an issue with the server at which the site is hosted (memory limits, execution times, etc.). Where should you start troubleshooting if you see this error on your WordPress site? Without a great deal of context, it can sometimes be frustrating and overwhelming where to even begin.
ERR_CONNECTION_TIMED_OUT error in Safari How to Fix the ERR_CONNECTION_TIMED_OUT Error