What configuration settings in AnyRouter might contribute to a 520 error with an empty response?

Incorrect upstream server addresses, port numbers, or protocol settings (HTTP vs. HTTPS) in AnyRouter's configuration are common causes. Also, check timeout settings. If AnyRouter's timeout is too short, it might give up before the upstream server can respond, resulting in a 520. Firewall rules blocking communication between AnyRouter and the upstream server are another potential issue.