I somehow managed to kill the etcd instance and cause the cluster to permanently fail because I restarted masters too many times in a test deployment.
I am honestly reconsidering my plan to use etcd for a few services
Discussion
I hit an edge case where I ran only with external IPs with the Hetzner CCM as well.
Somehow, the NodeHosts config in the integrated CoreDNS was not properly set by K3s because it wanted only internal IPs.
None of my nodes had internal IPs, so CoreDNS hung until I manually created the config entry
Other things include if you remove the IPv6 external address of a node in a dual-stack config, that node will go into a perpetual crash loop.
If you use Hetzner CCM and it is not set to dual-stack, it will take your entire cluster down.