Yes - so for a long time, skulls have been broken on Nightfalls. We have fixed this, but in doing so we had to deviate somewhat from the original contract. activityHash is still on the advisor contract, and it continues to point at the "generic" nightfall activity: the playlist, if you will. specificActivityHash is a new field that points to the specific Nightfall activity that will be performed when you jump into the Nightfall. The skullIndexes now work, but you have to index into the specificActivityHash's skulls in order to get at the correct data!