I kinda think it may be on the isp then, maybe a v6 routing issue? You could work around with an ipv4 tunnel, then route ipv6 through it. If that’s possible, I’ve never done it haha.
Yeah, ISP-related issue is all I can think of. I can connect to the server over v4 no problem, but the broken v6 connectivity to this particular endpoint is strange and nothing I’ve seen before…