Intermittent IPv6 connectivity on VPS

[z411 <z411%omaera.org@localhost>]

Hello,

I'm looking into learning IPv6 and I've managed to enable it on 2
machines, but not on my NetBSD one. It's also the only one on a VPS
provider that uses Virtulator, which I *think* may be the root cause.

I can ping my own interface, but when pinging an external IP (or even
the gateway) the ping is intermittent. It errors out with "No route to
host" for ~20 seconds, then starts working for ~30 seconds, then it
starts erroring out again, and the cycle repeats.

I found another NetBSD user [1] who seemed to found an issue with
Virtulator, because it blocks Neighbor Advertisements coming from IPs
other than the global unicast, and NetBSD apparently uses the local-link
address as a source [2].

I tried the patch [3] posted in that thread but it didn't fix it for me,
so maybe it's something else. Doing a tcpdump I didn't find a
solicitation response from my machine, but only from the router:

16:41:21.468335 0c:59:9c:8c:dc:e4 > 00:16:3e:1b:72:3a, ethertype IPv6
(0x86dd), length 86: (class 0xc0, hlim 255, next-header ICMPv6 (58)
payload length: 32) 2a06:a880:3::1 > 2a06:a880:3:27b4::1: [icmp6 sum ok]
ICMP6, neighbor advertisement, length 32, tgt is 2a06:a880:3::1, Flags
[router, solicited, override]

For reference, this is how I configured my interface:

ifconfig wm0 inet6 2a06:a880:3:27b4::1 prefixlen 64 alias
route add -inet6 default 2a06:a880:3::1 -connected -ifp wm0

Does this behavior sound familiar? How can I be troubleshoot the root
cause? I was going to open a ticket to the provider but as the NA patch
didn't work I can't be sure it's really on their end.

[1] https://www.unitedbsd.com/d/1491-ipv6-address-and-subnet-configuration
[2] https://marc.info/?l=netbsd-tech-net&m=173753439711511&w=2
[3] https://marc.info/?l=netbsd-tech-net&m=173758077609242&w=2