We're having the same issue. A bunch of IPv6 ranges aren't mapping to a location causing one of our CA rules to fail, causing a bunch of cranky users. I've been having to exclude huge swaths of IPv6 addresses to keep our users online. Our rule has been running for several months flawlessly.
Mostly, it appears to be cellular carriers - AT&T, Verizon, Comcast. I have a ticket in with MS, we'll see if that gets us anywhere.