If I dig my fqdn hostname from my freedombox it returns the local address.
If I dig my fqdn hostname from a DNS server it returns NXDOMAIN
My dynamic DNS system app says that it is updated recently and has the right IP address.
If I log in to my GnuDIP service page I see that my IP address is identified by GnuDIP server.
It sounds to me like the issue is that the sds-ip.de DNS records are not getting populated by the GnuDIP server.