Hey and welcome
Thanks for reporting him. I can confirm that the Blizzard WoW team are aware of this bug and an appearance fix will be issued in a subsequent patch. Whether this is days, weeks or months away I can't say, sorry.
The other common appearance bug we're aware of is that a number of transparent / ghostly tames have lost their transparency in the game. It seems to be NPCs where the base model isn't transparent, just that one particular skin - if the model is itself was designed to be transparent the NPCs seem to be fine. This is also a known bug, affecting a lot of NPCs, not just pets. They're aware of it and will fix it, but I don't have a time frame.