That likely means that you are have BESClient installed on some virtual machine and it is reporting data, but that VM is hosted on a hypervisor from which you are not collecting server data. It could be that you have more than one ESXi server, or some Hyper-V in addition to VMWare, etc. and you are retrieving VM Manager data from some of them but not all of them.
Whether that matters, depends on your licensing. Some licenses (such as IBM’s Subcapacity Licensing) allows you to license software based on how many cores the VMs are using rather than how many are installed on the hypervisor hosts. To track those licenses for compliance requires the management extender to track which VMs are running on which Hypervisor Hosts, and how many processors are allocated to those VMs.