`google_compute_subnetwork` `external_ipv6_prefix` of any value causes 20+ minutes delay to apply then an Error 503 Internal Error

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Terraform Version & Provider Version(s)

Terraform v1.9.4 on windows_amd64

provider registry.terraform.io/hashicorp/google v6.0.1

Affected Resource(s)

google_compute_subnetwork

Terraform Configuration

terraform {
    required_providers {
        google = {
            source = "hashicorp/google"
            version = "6.0.1"
        }
    }
}

provider "google" {
    project = "project-id"
    region = "us-central1"
    zone = "us-central1-a"
}

// ipv6

resource "google_compute_network" "network-dual" {
    name = "test"
    auto_create_subnetworks = false
}

resource "google_compute_subnetwork" "subnetwork-dual" {

    name = "test"

    ip_cidr_range = "10.0.0.0/22"

    stack_type = "IPV4_IPV6"
    ipv6_access_type = "EXTERNAL"
    external_ipv6_prefix = 128

    network = google_compute_network.network-dual.id
}

Debug Output

No response

Expected Behavior

A correctly made subnet, or an indication of what a valid input would be

Actual Behavior

Error: Error creating Subnetwork: googleapi: Error 503: Internal error. Please try again or contact Google Support. (Code: '62105D52989F6.7E40067.2A183273'), backendError

Steps to reproduce

terraform apply

Important Factoids

I tested with 0, 24, 32, 48, 64, 96, and 128

References