Ok, last night I read more about PKDNS and found out that you have to publish your DNS entries at intervals because the MAINLINE DHT also deletes the entries in the hash table at intervals. That's why you have to run a service that constantly republishes the DNS zone.
./pkdns-cli publish seed.txt dns.zone
Packet xiqz1bc7xmiw9kz8n8j6epbwnww59nibd9f7175cwd1jz6kmcdko
@ A 144.76.70.79
Announce every 60min. Stop with Ctrl-C...
2024-11-02 17:38:53.291982645 +01:00 Successfully announced.