The bug
The llamas don't spawn in the shattered savanna plateau even though they spawn in savanna plateau.
How to reproduce
Create a shattered savanna plateau buffet world, and try to look for llamas (or use the execute command to locate them). There will be absolutely no llamas, and instead there will be horses like there are in normal savanna biomes.
Linked issues
relates to 3
Comments 5
Confirmed for 1.13.2-pre1.
Confirmed for 1.13.2-pre2.
Can confirm for 1.16.5

This is fixed in 21w40a
It would make sense for llamas to spawn in shattered savanna plateaus, as they spawn in regular savanna plateaus. They don't spawn in regular savannas anyway, so they don't necessarily have to spawn in shattered savannas as well.