I was exploring the new snapshot with the caves and cliffs preview datapack and noticed that when flying in creative or spectator, the chunks would flicker and some wouldn't load at all. I have seen this issue been fixed in normal worlds but it continues to occur in worlds with extended height.

Edit: I noticed that when loading worlds with extended height the world loads very slowly in the beginning but as I start exploring the chunks load fine. I have attached the images of certain places where chunks don't load properly. This especially happens when flying in spectator mode