I think it's a local issue. Does the code work with both IPv4 and IPv6 (set the first line to AF_INET for IPv4)?
Yes, I do have setup one for IPv4 and one for IPv6, both were working on 24.11 for some time. The issue with IPv6 started after the upgrade to 25.3-BETA.
Parallel there are two (one IPv4 and one IPv6) setup for duckdns.org using the Custom/Custom v6 service, which are running fine too.