We have an application that sets the default JMX domain to our company prefix "com.build". Since STS4 is using JMX to provide the live hover support, it does not find any of the actuator endpoints because they are under a different domain. I am not sure you can detect the domain on startup (probably not), so this might just be a configuration property that is added to the tool: "Actuator JMX Domain" or maybe just something that is added to the documentation.

I was able to work around the problem by setting the "endpoints.jmx.domain" back to "org.springframework.boot".