Noise caves such as cheese caves, spaghetti caves, and noodle caves will generate below old chunks, but cave carvers will not. This makes old chunks with new caves seem empty, especially in spectator mode.
To reproduce, load a world in 1.17.1 and reenter it in the latest snapshot, saving your seed and location. Create another world in the latest snapshot with the same seed and go to the same location. The world from 1.17.1 will not have cave carvers below Y=0.