Disclaimer! This is using an unsupported change to vCenter and the setting also controls concurrent vMotions. Use this at your own risk. Always snapshot or backup your vCneter Server and database before attempting this change.
On the next screen add a new key config.vpxd.ResourceManager.maxCostPerHost and a value of more than 8. 8 is the current max.
So for example you want to clone 10 VM’s at once. You may want to max this value 20 as this does include vMotions.