[1.15.2] Custom mobs not spawning in custom biome

[Alex Sim]

I'm trying to port a dimension mod to 1.15.2;

 

I have only this one issue: mobs spawned with EntityClassification.MONSTER spawn like they should (at night or in caves), but mobs with EntityClassification.CREATURE do not spawn at all (and yes, I register the spawn with EntitySpawnPlacementRegistry) here is the function i use (code is in Kotlin, very similar to Java)

 

EntitySpawnPlacementRegistry.register(MY_ENTITY_TYPE, PlacementType.ON_GROUND, Heightmap.Type.MOTION_BLOCKING_NO_LEAVES, EntitySpawnPlacementRegistry.IPlacementPredicate({
	world, _, pos, _ -> world.getBlockState(pos.down()).run {this == Glacia.Blocks.GLACIAL_DIRT.stateSnowy || block == Blocks.GRASS_BLOCK} && world.getLightSubtracted(pos, 0) > 8;
}))

^ snippet from Glacia_Entity.kt

I call the `registerProperties()` function from my FMLCommonSetupEvent call and register the entities on my RegistryEvents class (the process might be a bit unusual, but it works, and i can spawn them with commands)

 

Here is how I add the spawns in my Biome constructor

 

this.addSpawn(EntityClassification.MONSTER, SpawnListEntry(EntityType.SLIME, 50, 4, 4))
this.addSpawn(EntityClassification.CREATURE, SpawnListEntry(Glacia.Entity.GLACIAL_TURTLE, 40, 4, 4))
this.addSpawn(EntityClassification.CREATURE, SpawnListEntry(Glacia.Entity.SABER_TOOTHED_CAT, 30, 4, 4))
this.addSpawn(EntityClassification.CREATURE, SpawnListEntry(Glacia.Entity.REINDEER, 25, 5, 8))
this.addSpawn(EntityClassification.CREATURE, SpawnListEntry(Glacia.Entity.PENGUIN, 20, 5, 8))
this.addSpawn(EntityClassification.MONSTER, SpawnListEntry(Glacia.Entity.GLACIAL_SEEKER, 100, 5, 8))

^ snippet from BiomeGlaciaPlains.kt

 

As I previously said, GLACIAL_SEEKER spawns correctly while the other custom mobs do not; am I missing something?

 

EDIT: if that can help, my biome uses a custom block as "grass", which I already added to the spawn conditions

Edited April 9, 2020 by Alex Sim