stack create failing with IpAddressAlreadyAllocatedClient error

Issue

• Creating application stack via heat template is failing with following error.

(overcloud) [stack@director 2020-0304]$ time openstack stack create -t ./spirent-vm-v2.yaml spirent-vnf1 --verbose --wait
START with options: [u'stack', u'create', u'-t', u'./spirent-vm-v2.yaml', u'spirent-vnf1', u'--verbose', u'--wait']
command: stack create -> heatclient.osc.v1.stack.CreateStack (auth=True)
Using auth plugin: password
2020-03-04 21:31:42Z [spirent-vnf1]: CREATE_IN_PROGRESS  Stack CREATE started
2020-03-04 21:31:42Z [spirent-vnf1.key_name]: CREATE_IN_PROGRESS  state changed
....
2020-03-04 21:31:57Z [spirent-vnf1.network-490]: CREATE_COMPLETE  state changed
2020-03-04 21:31:57Z [spirent-vnf1.resourcegroup]: CREATE_IN_PROGRESS  state changed
2020-03-04 21:31:57Z [spirent-vnf1.subnet-490]: CREATE_IN_PROGRESS  state changed
2020-03-04 21:31:57Z [spirent-vnf1.subnet-491]: CREATE_COMPLETE  state changed
2020-03-04 21:31:58Z [spirent-vnf1.subnet-490]: CREATE_COMPLETE  state changed
2020-03-04 21:32:14Z [spirent-vnf1.resourcegroup]: CREATE_FAILED  IpAddressAlreadyAllocatedClient: resources.resourcegroup.resources[0].resources.vTS1_eth0_mgmt_port: IP address 10.10.10.10 already allocated in subnet 2a70b802-c0f3-49b7-87af-1b00a513046c
Neutron server returns request_ids: ['req-2204fad8-87e3-46e4-87b
2020-03-04 21:32:14Z [spirent-vnf1]: CREATE_FAILED  Resource CREATE failed: IpAddressAlreadyAllocatedClient: resources.resourcegroup.resources[0].resources.vTS1_eth0_mgmt_port: IP address 10.10.10.10 already allocated in subnet 2a70b802-c0f3-49b7-87af-1b00a513046c
Neutron server returns request_ids: ['re

 Stack spirent-vnf1 CREATE_FAILED

END return value: 1

real    0m43.913s
user    0m1.112s
sys     0m0.244s

• Heat template looks like this:

  eth0_mgmt_fixed_ip:
    type: string
    default: "10.10.10.66"
    description: management-network/public-network/master-network eth0 IP address
[...]
      name: "spirent_vlan485_mgmt-subnet"
      cidr: 10.10.10.10/26
      enable_dhcp: true
      allocation_pools:
        - start: 10.10.10.65
          end: 10.10.10.123