For some time, I observed that Gammu test dashboard does not get updates from my Debian box. Looking the CTest logs, the problem was in using IPv6 even when the box does not have it enabled:
Failed to connect to 2001:1528:136:dead:beef::1003: Network is unreachable
Due to lack of time I ignored it, but it looks all what was needed is to update curl. The bug was caused by using c-ares resolver, which for some reason favors AAAA records even when the system has no IPv6.