Dual Pi-Hole Setup both suddenly stopped serving DNS on port 53 - Pi-holes can resolve DNS locally

Help
1

I spent all last night googling this, and could not seem to find something similar. This occurred without warning and without any that I made changes. I do have a cron job that runs pihole -up every 24 hours. The pi-holes are kept in sync with Gravity Sync. So I suspect root cause is either an update via cron, or gravity sync misbehaving.

Details

Raspberry Pi 3 - Primary DNS 192.168.1.9
Raspberry Pi 4 - Secondary DNS 192.168.1.8
DNS is resolved for each Pihole locally via the cloudflared daemon
Pi-holes are kept in sync with Gravity Sync GitHub - vmstan/gravity-sync: 💫 The easy way to synchronize the DNS configuration of two Pi-hole 5.x instances.
TLS is enabled for web interface
All services seem to be running
Port 53 is open and running on both piholes
Local DNS records that are served by the pihole are not resolvable.

Actual Behaviour:

No clients on network can resolve DNS
Local DNS addresses do not resolve
DNS seems to be "running" but not working

Debug Token:

https://tricorder.pi-hole.net/1px7K3kq/
https://tricorder.pi-hole.net/yLiuwbiK/

2

I think I found root cause - the Cloudflared Daemon is not resolving on either host suddenly. So something is amiss with DNS over HTTPS Since I had the upstream DNS Servers set to Custom 127.0.0.1:5053 the piholes could resolve via /etc/resolve.conf

Changing to using "regular" Cloudflared servers seems to have worked.