Still in the same boat. I reported this on the Customer Support forums last week:
https://us.forums.blizzard.com/en/wow/t/pocket-pet-portal-stopped-working/687999
It appears to have happened after I faction transferred my hunter. I am basically unable to do anything with the battle pet window. For example, it wants me to go to a Battle Pet Trainer to learn how to collect and fight with battle pets, then earn the achievements [Newbie] and [Just a Pup] to unlock the subsequent two slots.
The forum reply from the Blizzard Customer Service Rep said “…it has been identified as an issue, the Game Masters should be able to assist if they can confirm you’re affected.”, and that I should open a ticket.
The GM that addressed my ticket said “Right now we are receiving reports on this issue happening to some players in game, what we are asking is for you to submit a bug report.” Which I have already done…
I am not sure what to do now aside from sit and wait? The silliest part is I have a physical collectors edition sitting here, and I am not sure if I should active it yet because it comes with a pet that I can presumably not claim at the moment. Also, all this appears to have happened because I paid for a faction change.