Collision failing on fast moving object

Given this script, I used it on a cylinder moving across a field (it is suspended in the air, without gravity influence). Four static cubic colliders act as walls, defining a simple rectangular bound. The cylinder has a capsule collider and a physics material with bounciness 1. It has a small mass (0.1) and a little drag (0.01).

 using UnityEngine;
 using System.Collections;
 
 public class PlayerMovement : MonoBehaviour {
     private float x;
     private float z;
     public float speed=1200f;
 
     // Use this for initialization
     void Start () {
         
     }
     
     // Update is called once per frame
     void FixedUpdate () {
         x= Input.GetAxis("Horizontal")*speed*Time.deltaTime;
         z= Input.GetAxis("Vertical")*speed*Time.deltaTime;
         if (Mathf.Abs(rigidbody.velocity.x)<90&&Mathf.Abs(rigidbody.velocity.y)<90)
         {
             rigidbody.AddForce (x,0,z);
         }
     }
     
     void Update (){
         print(rigidbody.velocity);
     }
 }
 

Problem is, with speed set at 1200 (which is fast and reactive, considering the Time.deltaTime multiplayer), the collider often fails, making the cylinder pass through the wall. I tried to divide the fixed timestamp by half, with no result. The object is quite fast, but it's certainly not a bullet (it is meant to be controlled by the player), so these errors seem quite strange to me.

Is there anything else I can do to improve the collision detection? I tried to set the rigidbody parameter as Continuous Dynamic, with no results whatsoever.