When creating a new 1.17 world with the Caves and Cliffs Preview datapack, the world generates fine with the new cave generation and new height limits. When uploading this same world to realms, the generation doesn't work and the height limits are reset to their regular values.

The seed for this world is: 7980569888039328864

To get to the location in the screenshot use
/tp @s -165 24 -441 -88.1 45.3

How to reproduce
1.) Create a new world with the preview datapack released in Snapshot 21w20a
2.) Generate new chunks and find some cool cave generation in spectator mode
3.) Go to realms and upload this world into one of the 3 realm world slots.
4.) Join this realm and notice that the world is reverted and the new generation doesn't work.