It would be useful to capture a thread dump in JDR reports, to see any potential problems there.

If the server is responsive, it can be done via /core-service=platform-mbean/type=threading:dump-all-threads(locked-monitors=true,locked-synchronizers=true)

If the server is unresponsive, it may be able to be done by JVM specific functionality, such as using tools.jar if on Oracle/OpenJDK as jstack does.