Google Cloud DNS Publc Records Not Available After 2 weeks

I have set up Cloud DNS with a public DNS zone in a Google Cloud project using Google Terraform Modules (https://github.com/terraform-google-modules/terraform-google-cloud-dns). I have added the custom name servers to Google Domains where the domain is owned.

After about 2 weeks, no records have yet been propagated to the public internet. The DS Key record is the only record that running Dig against my domain finds, and that is defined in Google Domains, not Google Cloud DNS.

I have a few TXT records, an A record, a few CNAMES, an NS record with the Cloud DNS nameservers, and a default SOA record in Cloud DNS.

The nameserver record is based on:

How can I determine why this is not working?

I commented out my dns terraform and applied terraform to delete the dns zone.

I then uncommented and reapplied my terraform, and that almost immediately worked after updating the custom dns records in Google Domains.

Weird. No Idea why that worked, nothing changed, except instead of a1-a4 for nameservers it is now c1-c4.