This network in question is a fully functional NAT64/DNS64 network.
The auto-update function does not work. It give a curl error: "couldn't connect to host".
Running wireshark, I can see it does a DNS query just for the A record of 'notepad-plus-plus.org'.
That gets answered correctly (18.104.22.168), but since IPv4 is not available, the error occurs.
Had the app been to use IPv6, thing would have worked because of NAT64:
Pinging notepad-plus-plus.org [2001:610:148:ffff:b0b0:0:d455:9e04] with 32 byte
Reply from 2001:610:148:ffff:b0b0:0:d455:9e04: time=23ms
Ping statistics for 2001:610:148:ffff:b0b0:0:d455:9e04:
Packets: Sent = 1, Received = 1, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 23ms, Maximum = 23ms, Average = 23ms
See https://confluence.terena.org/display/~visser/Free+IPv6+wireless+network for more details on this network.