From the original message:
I've setup a ping probe (ID#2143865) to ipv6.google.com and it's consistently giving 1msec RTT RTT I get on the CPE the probe is connected to 0 2a00:1450:4003:806::200e 56 59 12ms echo reply
My guess is that maybe the probe was set up to use a different DNS resolver than the CPE, and it got a different IPv6 instead of 2a00:1450:4003:806::200e.
Indeed the probe pinged 2a00:1450:4004:801::200e and not the address above. I have no idea if that's the root cause for this, but it's certainly a different target. It could be the same DNS resolver but it got different answers at different times? I set up one-off traceroutes 2144086 (ICMP) and 2144089 (UDP) and they seem quite reasonable to me (5 hops, ~1.2ms to target). Robert