An error similar to the following is displayed in the logs:
Remote Server: XX.XXX.XXX.XXX
Fatal: Call to virConnectOpen failed: Cannot recv data: Host key verification failed.: Connection reset by peer
The issue can be resolved by adding the Hypervisor's RSA key to the known_hosts file for the onapp user on the Control Panel. The easiest way to do this is to SSH into the Control Panel, switch to the onapp user, then SSH into the Hypervisor shown in the error log. It will ask if you'd like to add the Hypervisor's key to the known_hosts file.