检查有问题的Prefab发现，某个GameObject上出现了2组 MeshRenderer 和 MeshFilter，去掉多余的一组，该问题解决。

The problem was that one of the enemies had 2 renders attached to the same gameobject. After removing one of them, the problem was fixed.

注意： 一个游戏对象上，某些组件可以挂载多个，而某些组件只能挂载一个。

Ref: https://forum.unity.com/threads/errors-in-unity2017-1-0f3.482881/