Rigidbody randomly fall through floor

Hi everyone I had a weird issue with my project. When I make my character jump, he randomly fall through the floor like this: http://plays.tv/video/588b59f23a5950461c/wtf-unity

I don't understand why it's happening.

Here is the script of the character controller that is affecting this rigibody:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerController : MonoBehaviour {
 
     float move;
     public float moveSpeed = 12f;
 
     public bool isJumping = false;
     public bool grounded =  false;
     public bool toped = false;
 
     float jumpForce = 175f;
     float jumpTime;
     float jumpMaxTime = 0.3f;
 
 
     public GameObject gameController; // On récupère le GameObject contenant le GameController
     GameController gameControllerScript; // Variable pour stocker le script GameController
 
 
     // Use this for initialization
     void Start () {
         gameControllerScript = gameController.GetComponent<GameController>(); //On récupère le script GameController
     }
     
     // Update is called once per frame
     void Update () {
 
         move = Input.GetAxis("Horizontal");
         GetComponent<Rigidbody>().velocity = new Vector3 ( move*moveSpeed , GetComponent<Rigidbody>().velocity.y - gameControllerScript.gravity, GetComponent<Rigidbody>().velocity.z);
         print (grounded);
 
 
 
         if (grounded) {
             
             if (Input.GetButtonDown ("Jump")) 
             {
                 jumpTime = 0f;
                 isJumping = true;
             }
         }
 
         if (isJumping) {
             
             jumpTime+= Time.deltaTime;
 
             if (((toped) || jumpTime >= jumpMaxTime || Input.GetButtonUp("Jump")) & (jumpTime > 0.3f)) {
                 isJumping = false;
             }
 
             GetComponent<Rigidbody>().AddForce(Vector3.up * jumpForce);
         }
 
     
     }
 
 }
 

And here is some screenshots from Unity:

What is happening and what can I do to fix this? If you have any things you can say about my code don't hesitate as well if you have any advice :)