your DNSSEC is broken - https://check-your-website.server-daten.de/?q=cepforum.com
Your parent zone has two DS RR, but your zone doesn't have the required DNSKEY set.
Same result using DNSSEC Analyzer - cepforum.com
So there is no chain of trust, so it's not possible to find a signed A- or AAAA-record (ip address).
Did you change your hoster? Perhaps your old hoster had DNSSEC support, your new not -> your new hoster must remove the DS records in the parent zone or add a correct DNSSEC to your zone.
PS: I've moved your question to a new topic. The other topic - there were buggy name servers. Your topic - DNSSEC is broken.