Nautili spawned as a result of a player breeding two other nautili can despawn

Steps to Reproduce:

1. Summon two Nautili and tame then breed them with Pufferfish

2. (Optional) Run the command: /tick rate 10000

3. Wait for the baby to grow up then fly 200 blocks away from them

4. Fly back

Observed Results:  

Only the parent Nautili remain, the grown-up child Nautilus has despawned

Expected Results:  

Nautili spawned as a result of breeding are persistent