Goats are not spawning in mountains.

Goats compete for cap space with other animals. If you have naturally-spawned tamed pets with you, or a collection of naturally spawned animals, those could be filling the surface animal cap.

Could you provide a copy of the affected world?

Cleaning up old tickets: This ticket had been set to 'Awaiting Response', but has not received a response from the reporter (~3 months+) so is being closed as Incomplete. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines which includes steps to reproduce the problem.

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