This is a known issue affecting vCenter Server 7.0 U2 and is resolved in 7.0 U3.
Workaround:
To workaround this issue, access vCenter using a fully qualified domain name instead of IP address.
Additionally, if the Hostname within the VAMI is short, update the hostname to FQDN.
Note: - If the vCenter Version is 7.0 U3 Version and still facing the issue, then make sure to login via [email protected] and not with any AD User credentials and retry the Native Key Provider backup.