hetzner default nameservers not always resolving

I don't understand why you are still trying to use the Hetzner DNS servers if they are demonstrably not working correctly. Just update your /etc/resolv.conf appropriately and get on with your life.

I usually chuck 8.8.8.8 and 8.8.4.4 (or 2001:4860:4860::8888, 2001:4860:4860::8844) in and forget about it.