VMware is aware of this issue and working to resolve this in a future release.
Workaround:
If the vNIC is on a Virtual Standard Switch (vSS), you can modify the MAC address via the ESXi Host Client.
Note: this method will not work with vNICs on a Virtual Distributed Switch (vDS).
You can temporarily change the portgroup for the vNIC to one on a vSS in order to use the workaround below, then change it back to the original portgroup on the vDS after you complete the MAC change. This portgroup change should be done from vCenter, not via the ESXi Host Client.
- Power off the VM.
- Right-click the Virtual Machine and select Edit Settings > Network Adapter > MAC Address, then change the dropdown option from Automatic to Manual and configure the required MAC Address and click SAVE.
- Power on the VM.