Following up on a two year old thread, one of my clients just hit this
problem. The failure is not that www.pay.gov is not reachable over ipv6
(2605:3100:fffd:100::15). They accept (TCP handshake) the port 443
connection, but the connection then hangs waiting for the TLS handshake.
openssl s_client -connect www.pay.gov:443
openssl s_client -servername www.pay.gov -connect 18.104.22.168:443
Browsers (at least firefox) see that as a very slow site, and it does
not trigger their happy eyeballs fast failover to ipv4.