The Java Agent comes with Network Visibility enabled by default. This error appears if the Network Visibility Agent process is not running on the host:

[AD Thread Pool-Global0] 27 Apr 2022 07:35:28,539 ERROR NetVizAgentRequest - Fatal transport error while connecting to URL http://127.0.0.1:3892/api/agentinfo?timestamp=0&agentType=APP_AGENT&agentVersion=1.11.4: org.apache.http.conn.HttpHostConnectException: Connect to 127.0.0.1:3892 [/127.0.0.1] failed: Connection refused (Connection refused)

If Network Visibility is not required in your environment, you can ignore this error.