Currently tserv11.ams1 (Amsterdam, NL) seems to be down. I did notice this happened a couple of times before.
On one firewall there's 67% packet loss and on mine at home there's 71% at the moment.
Would it be an idea to hop to another tunnel server? Eg Berlin, DE?
If you do that, you'll have to create a new tunnel and you'll have to use a different /64 as the /64s and /48s are locked to the tunnel location you signed up with.
tserv11.ams1 has been been having problems with jitter and packet loss for around a year now. It's a shame nobody is willing to look into it :(, but I'm aware that it's a free service.
I switched my tunnel over to tserv1.lon2 and that solved it. At the expense of higher latency.
I have been looking into VPS providers that offer v6 prefixes and using it as a 6in4 tunnel, but I haven't had any luck.