The bug

Baby ocelots spawned naturally prevent the parent ocelot from spawning.

Note: This bug is currently blocked by MC-103516 which allows the parent ocelot to spawn.

How to reproduce

1. Create a Superflat world with the following preset

   70*minecraft:stone,minecraft:grass_block;minecraft:jungle;
   

   Note: The 70 layers of stone are required because ocelots only spawn above sea level.

2. Setup a repeating command block and two chain command blocks behind it with the following commands

   /execute as @e[type=!player] if entity @s[type=!ocelot] run kill
   

   /execute as @e[type=ocelot] run data modify entity @s NoAI set value 1b
   

   /execute as @e[type=ocelot,nbt={Age:-24000}] run data modify entity @s Glowing set value 1b
   

3. Move around and look at the naturally spawned baby ocelots
   → You will notice that they are always spawned without parent

Code analysis

Outdated

Based on 1.11.2 decompiled using MCP 9.35 rc1

The problem is that the method net.minecraft.entity.passive.EntityOcelot.onInitialSpawn(DifficultyInstance, IEntityLivingData) spawns the baby ocelots at the same position the parent ocelot would spawn. Because of that the parent would collide with them and is therefor not spawned.