Recent discovery.
Looks like Chrome on windows now ignores the prefix policy.
So by default IPv6 is preferenced which should mean on dual stack IPv6 will nearly always be used, and if the policy is reversed vice versa.
Since my IPv6 is via a 200mbit tunnel, I preference IPv4, and discovered Chrome, Edge (and I assume all forks) instead seem to be either randomising the stack or got some kind of internal algorithm, probably the latter. So they breaching RFC.
The IPv6 test website if I refresh spam will actually seemingly randomly flip from "your browser priorities IPv6" and "your browser prioritises IPv4".
Firefox behaves normally.
It could be a bug but with the attitude of web browser developers these days where they want to control everything instead of the device admin, it wouldnt surprise me if its deliberate.
Havent found any reference to the change on the internet or a way to override the behaviour. So really bad.
Also affects Steam as Steam uses Chrome framework.
Someone on Reddit verified the behaviour.