Automated RJMX testing on JMC sometimes fails and I narrowed it down to be related to a specific OS version.
On macOS 10.13.1 and 10.13.2 (High Sierra) the OperatingSystem MBean intermittently returns a "NaN" double value for the attribute SystemCpuLoad.

This can be reproduced with JDK 9 as well as JDK 8.