If I’m not mistaken OnControllerColliderHIt() does not fire when two character controllers collide. As the function name implies, it’s controller and collider. And OnCollisionEnter() does not work reliably with character controllers. At least from my previous experience with this a year ago.
So what would be the function you would want to use when two characterControllers collide? I’m having the same issue. OnControllerColliderHit does recognize a collision happens, but only when they begin to move away from each other in my case. Could this be a problem with the sizes of the collision boxes?