Error defining ALB with 2 subnets in differents AZ - amazon-web-services

Question

I'm designing a cloudformation to deploy ALB and i got an error that says:
At least two subnets in two different Availability Zones must be specified (Service: AmazonElasticLoadBalancingV2; Status Code: 400; Error Code: ValidationError;
These network was created by other Cloudformation. And now, i go to VPC / SUbnets and i see both created.
The part of code where im defining the subnets in ELB creation is this:
"Subnets": [
{
"Fn::ImportValue": {
"Fn::Join": [
"-",
[
{
"Ref": "ParentSubnetStackName"
},
"PublicSubnet1ID"
]
]
},
"Fn::ImportValue": {
"Fn::Join": [
"-",
[
{
"Ref": "ParentSubnetStackName"
},
"PrivateSubnet2ID"
]
]
}
}
],
The only thing that i think that could be a problem is than im importing by other stack than i dont executing at the same time of this cloudformation.. I don't know if there could be a problem, because the Subnets are created at this moment for sure and they belong to differents AZ.
EDIT:
#jogold The CF is too long. I attach here a piece of the code
"PublicSubnet1": {
"Type": "AWS::EC2::Subnet",
"Properties": {
"VpcId": {
"Fn::ImportValue": {
"Fn::Join": [
"-",
[
{
"Ref": "ParentStackName"
},
"VPCID"
]
]
}
},
"CidrBlock": {
"Ref": "PublicSubnet1CIDR"
},
"AvailabilityZone": {
"Ref": "AZ1"
},
"Tags": [
{
"Key": "Name",
"Value": {
"Fn::Join": [
"-",
[
{
"Ref": "AWS::StackName"
},
"PublicSubnet1"
]
]
}
}
]
}
And after in the outputs i export it:
"PublicSubnet1": {
"Type": "AWS::EC2::Subnet",
"Properties": {
"VpcId": {
"Fn::ImportValue": {
"Fn::Join": [
"-",
[
{
"Ref": "ParentStackName"
},
"VPCID"
]
]
}
},
"CidrBlock": {
"Ref": "PublicSubnet1CIDR"
},
"AvailabilityZone": {
"Ref": "AZ1"
},
"Tags": [
{
"Key": "Name",
"Value": {
"Fn::Join": [
"-",
[
{
"Ref": "AWS::StackName"
},
"PublicSubnet1"
]
]
}
}
]
}
All the subnets are created bye the same way.