Creatures won't mate, the fertilized egg died, or a pregnancy was lost

• Both creatures look ready, but nothing happens: hearts show on one and not the other, or the mating progress never moves.
• A fertilized egg's health falls until the egg is destroyed. On ASA, eggs once sank into the floor after a restart (fixed in 32.12).
• A gestation ended without a baby.

A pair mates only when both are the same species and of opposite sexes, within mating range of each other, not neutered or spayed, not following anyone, not on a mating cooldown, and with wandering or mating switched on. On ASA, since January 2026, a male and a female mate only when mating is enabled on both of them. If the tribe or the server is at its tame limit, the pair refuses to mate until a slot is free (see the guide Tame limit reached).

Progress is fragile: if a wandering pair moves out of range, mating stops and the progress resets. After mating, a female cannot mate again until her mating interval has passed. That timer keeps ticking while she is in a Cryopod (fixed in ASA 33.11), but transferring the pod to another map resets it.

A fertilized egg must be kept inside the temperature range of its species; outside it, the egg loses "Fertilized Egg Health" and is destroyed at zero. A gestating mother put into a Cryopod loses the pregnancy.

Players also report pairs whose wandering and mating toggles seem stuck, pairs that would not mate near a drop, a cooldown after a transfer that the screen did not show, and variants that would not pair with each other: spawned with wild-tamed, or modded with vanilla.