You converted a VPC from auto mode to custom mode and some Deployment Manager templates stopped working. How do you resolve it?

When converting a VPC from auto mode to custom mode, the automatically created subnets are removed, and you must manually define subnets. Deployment Manager templates that previously relied on the implicit naming or existence of auto-mode subnets will fail because those subnets no longer exist. To resolve this, you must update the Deployment Manager templates to explicitly reference the new, custom-defined subnet names and network configurations. IAM roles, firewall rules, and Cloud Armor whitelists are not directly related to how Deployment Manager identifies and provisions resources within a custom mode VPC. The issue stems from the templates' internal references to network resources, not access permissions or security policies.