MacBook wifi issues - ipv6 vs ipv4

Hi,

I am using an Airport Extreme last edition, software 7.7.3, to distribute my Internet Provider's connection. The router is doing DHCP, the Airport Extreme is only a wifi router.

I have many devices connecting happily to the Airport (iPhone, printers, my macbook), however my friend's macbook 13' sometimes fail to connect to internet. I can't know for sure it connects to the Airport at all, but it is seems to because it has an IPv6 address. I read somewhere on a forum that it could be linked to ipv6. And indeed when I change the Airport settings to "Link-local only", it connects in IPv4 and it works like a charm.

Any idea if this is a macOS bug or Airport bug Apple is going to address ?

Thanks.