Warlock pet action bar bugs out with quests gaining a NPC follower. Action bar stops working. Also at the same time Loss of Pet spell book. your pet becomes lock to the last stance. Workaround is to Dismiss pet hearth to org log out to get it back 50% of the time.
I don’t know why but I’ve found a more reliable pet bar return is in an Inn outside of a major city. I have have a 49 Warlock and 32 Hunter.