"engine_requestId"
"The proxy server did not understand the request"
"No appropriate upstream server is available to handle this request"
"Unable to proxy request because the upstream server does not support "
"The client did not complete the request in time"
"An unexpected internal error has occurred"
"An error occurred while connecting to the upstream server"
"Connection to the upstream server timed out"
"Connection to the upstream server closed unexpectedly"
"An error occurred in the connection to the upstream server"
"Invalid HTTP response from upstream server"
"The upstream server took too long to respond"