When going for Sacrifice objectives (at least against Embermaw Hellion, but possibly others), there seems to be a bug in which destroyed creatures are often not counted as having been destroyed. At first I thought it was just tokens, like those produced through Murder Investigation, but even creatures cast from my hand aren’t always counted when they are destroyed.
Also, once I finally completed the objective and won the battle, I didn’t get the reward from it, and it didn’t register as having been completed.