Почему в OnCollisionEnter(Collision other) other.collider.gameObject
и other.gameObject указывают на разные объекты?
Может поэтому
In contrast to OnTriggerEnter, OnCollisionEnter is passed the Collision class and not a Collider. The Collision class contains information, for example, about contact points and impact velocity. Notes: Collision events are only sent if one of the colliders also has a non-kinematic rigidbody attached. Collision events will be sent to disabled MonoBehaviours, to allow enabling Behaviours in response to collisions.