This is a bug on Blizzard's end. We're not sure what percentage of users it's effecting, but keep in mind that many users are unaffected. So removing the option for everyone seems a little extreme.
For those of you who are dealing with this bug, we strongly suggest using the WarcraftPets Express
addon to update your collection. It requires a few more steps, but it's a great substitute until Blizzard corrects this issue on their end.