Well, even when ISPs are dilligent in deploying IPv6, they still have to deal with troublesome end-user hardware that can't just be replaced overnight. For exa

Well, even when ISPs are dilligent in deploying IPv6, they still have to deal with troublesome end-user hardware that can't just be replaced overnight. For example, here in Portugal the largest ISP (MEO) has had a wide deployment of IPv6 for many years. However, it's (up to very recently) main end-user router supplier (Thomson/Technicolor) has also had chronic IPv6 bugs in its firmware(1). MEO enables IPv6 by default nevertheless, but if you're an advanced user you'll have a hard time overlooking the random connection failures to IPv6 destinations. (1) Specifically, it resets the flow label field randomly when it is non-zero (the case with most recent versions of Linux, macOS and, I guess, Windows). Turns out the flow label is taken into consideration by many load balancers so, if it changes mid-connection, your packets may end up in a server that has no knowledge of you and you get a connection reset.