It seems to be intermittent? I can access it sometimes and other times I cant. When I cant unbound logs this
2024-03-26T11:14:08-04:00 Error unbound [20503:2] error: SERVFAIL : all servers for this domain failed, at zone duckdns.org. no server to query nameserver addresses not usable
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.