Result:

1. latest.log is multiple MB big as

[...] [Render thread/WARN]: Received invalid biome id: -1

is printed in a loop.

2. Jungle Biome the player spawns in turns to Ocean Biome

Steps to reproduce:

1. Install 21w16a, as well as (fitting) Caves and Clives preview datapack, no other ressource packs
2. Generate new world using the datapack and the seed -8460974445134698796
3. Quit world
4. Open world again

Attachments:

1. screenshot of f3 and seed
2. logfile (50MB uncompressed)