Question Animator problem Unity

Hello, I wish you good work. I have a problem related to Unity's animator part. As seen in the video in the link I posted, the characters initially perform their normal running animation movements, but then they fall. What is the reason of this? I am using the raycast method for the enemy ai that if they see the player clear distance they start running towards him.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.AI;
5.  
6.  
7. public class DüşmanAI : MonoBehaviour
8. {
9.     public NavMeshAgent enemy;
10.     public GameObject player;
11.     Animator animator;
12.     float distance = 100f;
13.    
14.     public LayerMask hedef;
15.  
16.     Ray ray;
17.     RaycastHit hit;
18.     // Start is called before the first frame update
19.     void Start()
20.     {
21.         animator= GetComponent<Animator>();
22.     }
23.     void check()
24.     {
25.         if (Physics.Raycast(transform.position, transform.forward, out  hit, distance) )
26.         {
27.  
28.            
29.  
30.         }
31.        
32.        
33.        
34.     }
35.  
36.     // Update is called once per frame
37.     void Update()
38.     {
39.         enemy.SetDestination(player.transform.position);
40.         animator.SetBool("koşma", true);
41.         //check();
42.  
43.     }
44. }
45.