After completing the first Illidan Book of Heroes fight with Arthas, they repeat the dialogue between the two of them four times. It should be only once.
Technical Details:
iPhone Xs
iOS 17.4.1
Hearthstone Client 29.0.195635
Still a bug as of 2025. Activision-Blizzard doesn’t care about sunset modes like Adventures so don’t hold out on this ever getting fixed.