The correct answer is B. Missing license.
Some hypervisor features may require a valid license to work properly. If the license is missing, expired, or invalid, the hypervisor may not be able to use those features or may operate in a reduced functionality mode. For example, some features of Hyper-V, such as live migration, replication, and failover clustering, require a license for Windows Server or Windows 10 Enterprise1. Similarly, some features of VMware ESXi, such as vMotion, Storage vMotion, and Fault Tolerance, require a license for VMware vSphere2.
Therefore, if a cloud administrator deployed new hosts in a private cloud and found that some of the hypervisor features did not seem to be working after a few months elapsed, the most likely cause was a missing license. The administrator should check the license status of the hypervisor and renew or activate the license if needed.
Incorrect permissions are not a likely cause of the issue, as they would affect the access to the hypervisor or its resources, not the functionality of the hypervisor itself. Incorrect tags are also not a likely cause of the issue, as they are used for identification and classification of resources, not for enabling or disabling features. Oversubscription is not a likely cause of the issue either, as it would affect the performance or availability of the resources, not the functionality of the hypervisor itself.