I’m noticing a slightly different pattern. I’m based in the UK. I believe it is the hops between the UK and US causing the problem.
I have two network providers. I have two ntp servers. I run both IPv4 and IPv6. I present both servers on both providers.
The first provider has a great reputation and provides native IPv6. On IPv4 that provider has struggled to stay above a score of 10 over the past few days. That same provider on IPv6 has consistently scored 20 for days.
The second provider, more of a residential broadband offering, has consistently scored 20 for days.
The paths taken from the monitor to my hosts are different for the two providers.
In my case, I suspect it is a Tier 1 between the UK and US dropping UDP as some kind of <> mitigation. I see less packet loss on protocol 13 (daytime) UDP and protocol 37 (Time) UDP. And no loss for those old protocols with TCP.
So there appears to be a difference between IPv4 and IPv6 (not commenting on 6in4) when comparing network providers. I’m using AS org as a proxy for network provider.
My first provider has a total of 25 hosts in the UK pool (IPv4 and IPv6). For that provider, across both IPv4 and IPv6, the average score is 9.72. For that same provider, the average IPv4 score is 2.74. And for IPv6, the average is 17.58.
AS Org combined IPv4 and IPv6:
AS Org IPv4:
AS Org IPv6: