Played the rouge legendary Anub’Arak and it died. It summoned a 4/4 as expected. But did not return to my hand.
I have not attempted to recreate it yet. But if you could investigate and check that the card isn’t bugged.
It had a change in the background last year to change how other cards copy it’s deathrattle. It used to work that the card that copied the effect would return it’s self. Now it works that the card will return a copy of Anub’Arak to you hand.
I think this is likely where the error is occurring. If you can run it in a test environment to see if it behaves as expected please.
Edit: Recreated it. Anub’Arak is there in hand but the card does not appear. It’s a visual glitch. It can still be played by dragging it’s card on to the battlefield. And it also is restored after you play secret passage.