It is possible for a Monitor belonging to HealthCheckMonitor to throw an unchecked exception that bubbles back up to the Web tier. In the default configuration, this results in a 200 OK response with a user-friendly error page containing a stack trace. This violates the contract of the health check controller where HTTP status codes above 200 indicate a problem. In this case there is a false negative since there is indeed a problem with a monitor, yet the container reports 200 OK.
HealthCheckMonitor needs additional error checking to trap unchecked exceptions and report the ERROR status (500).