Yes, so far we’ve confirmed this with Jggles and Trootie. Haven’t seen it mentioned for Ruffle or Sinheart yet. If you’ve gotten the covenant pet and have confirmed it’s slotted but not showing up in the battle, be sure to head over to the Bug Report forums. Here’s a thread someone else already started on it, at least for Jggles:
https://us.forums.blizzard.com/en/wow/t/jggles-necrolord-battle-pet/847177
The more attention we throw at it, even if you’re just confirming the mentioned covenants again, might get a quicker response to a fix.
eta: lol at not even being able to type out the Necrolord Covenant pet that Blizzard itself named 