From 21:57 onwards, an outage was occurred to DNSSEC signing.
It is unclear to what extent this problem affected the availability of these services. The signature was renewed during the night leading into Wednesday, thereby resolving the issue. The entire .de zone (mainly DNSSEC) was affected by this incident.
Source: DENIC – https://blog.denic.de/en/technical-issue-with-de-domains-resolved/