Hey,
see "IPv6 broken on Hetzner.de vServer OpenBSD 6.3 / amd64" on bugs@
I'm pretty sure hetzner sets a static route to your link local address for
the /64 they assign to you.
Since the the link local address changes with RFC 7217 you blackhole the /64...
you are right. It works fine when I disable RFC 7217 via -soii in my
hostname.* file. I am going to open a ticket with Hetzner so that they
can fix there routing. Because i asume using the -soii will not be a
solution for the next couple of years.
Thanks for helping me!
Greetings
Leo