Nostalrius Begins - Quality wow vanilla realm (1.12)

I recently tamed my first pet on a hunter but when I killed a yellow lvl npc the pets xp bar did not change at all (by extension the pet is also stuck on the lowest loyalty level as well). I have tried relogging and dismissing/calling pet but the issue remains.

EDIT: I leveled up once so im 1 higher then the pet then i started to get xp.

Thanks for telling it. I had the same problem, Im at same level as my pet right now and didnt't get any xp.
So i was searching around and found this post