I selfhost some tools and use duckdns for names resolution but it does not seem to be working today. My ISP updated some things on there end last night and I updated my local unbound server so I’m not sure which if either of these is also playing a role but I cant seem to access duckdns. I have tried to connect to it on my phone network outside of my isp’s control and cant which leads me to believe that duckdns is down?
I believe the nameservers are what respond to domain resolution requests. Nameservers not responding could mean they are down. If there’s no backup and the domain is resolved using one of those servers, then that might explain it not working.