FabricVmCreationError

I used a custom template to create a deployment, which succeeded yesterday.
The same template today fails with the following message:

{
"code": "DeploymentFailed",
"message": "At least one resource deployment operation failed. Please list deployment operations for details. Please see https://aka.ms/arm-debug for usage details.",
"details": [
{
"code": "Conflict",
"message": "{\r\n \"status\": \"Failed\",\r\n \"error\": {\r\n \"code\": \"ResourceDeploymentFailure\",\r\n \"message\": \"The resource operation completed with terminal provisioning state 'Failed'.\",\r\n \"details\": [\r\n {\r\n \"code\": \"FabricVmCreationError\",\r\n \"message\": \"Failed to create VM 'NetScaler-VPX-Express' \"\r\n }\r\n ]\r\n }\r\n}"
}
]
}

Have any idea what may be the cause of this instability in deployments?

Start with the custom ARM template deployment and the ARM debug guidance in the issue, then inspect deployment operations for the FabricVmCreationError affecting NetScaler-VPX-Express. Done means identifying a reproducible cause and documenting a concrete template or deployment change that prevents the VM creation failure.

Written by the indexing model from the issue text.