after i while of playing around with spawns and looking around the world via datapacks, i discovered that groups of rabbits only spawn one adult, maybe this is a bug caused with the new feature of groups sometimes spawning babies 

no matter the number of rabbits it's always only one adult 

How to reproduce
1.- use the datapack .zip below and create a single biome world of plains
2.- fly around and search for rabbits 
3.- the minimun amount of rabbits set with the datapack is 3 and the maximum is 5

1.- or you could go in a vanilla world and search for a deserts, since is the only biome were only rabbits spawns and see it by yourself