I wasn't able to connect/ping anywhere via IPv6. It was weird since 'curl -6v $target' would just hang, ping would say `sendmsg not permitted`. `ip addr; ip -6 route` showed the right settings, `sysctl -a | grep disable_ipv6` was fine, but packet tracing on the interface had total radio silence outside ipv4.
Long story short, `ip6tables -L` showed `OUTPUT (policy DROP)` which I traced back to this line in /etc/default/ufw:
IPV6=disable
It only took a few hours to figure out. Isn't Linux fun?