While adding doors to the Unity asset RFPS Prefab, I ran into the problem of the NPCs being able to walk through non-trigger colliders despite being properly configured with layers, physics, and colliders of their own.
The problem with RFPS Prefab’s stock NPC prefabs is that they have a kinematic rigid body component by default. This is improper, because they are supposed to be moving objects. This problem is easily fixed by setting RigidBody’s component “Is Kinematic” to disabled or unchecked. I hope this saves a few people my frustration.