All Duke script code has been changed to use strings as sound names now, just like GZDoom these will be looked up at compile time.
Original Duke sound indices still exist but are now being managed as resource IDs, not sound engine indices anymore.
Parts of the sound system treat entry 0 as "no sound" so nothing placed there would play.
This made the one custom sound in "The Way of Ira" not play because as the last sound being defined it ended up in the first, invalid slot.