Character Position Moved after Animation assigned

My character position is moved after an animation is assigned.

The character GameObject is assigned with Animation, RigidBody, Capsule Collider and a C# Script Component.

The C# Script (animation part) is as follow:

 public class MyCharacter : MonoBehaviour {
         // Animations
     public AnimationClip idleAnimation;
     public AnimationClip slideAnimation;
     public AnimationClip runAnimation;
     public AnimationClip jumpPoseAnimation;
     private Animation charAnimation;
     
     enum CharacterState {
         Idle = 0,
         Running = 1,
         Sliding = 2,
         Jumping = 3,
     }
     
     private CharacterState charState;
 
     void Start () {
         charState = CharacterState.Running;
         charAnimation = gameObject.GetComponent<Animation>();
         if(!charAnimation) {
             Debug.Log("No Animation Component.");
         } else {
             AnimationEvent syncRunEvent = new AnimationEvent();
             syncRunEvent.time = runAnimation.length;
             syncRunEvent.functionName = "SyncRunAnimation";
             runAnimation.AddEvent(syncRunEvent);
         }
     }
 
         void Update () {
                 // Animations
         if(charAnimation) {
             if(charState == CharacterState.Jumping) {
                 charAnimation.CrossFade(jumpPoseAnimation.name);
             } else if(charState == CharacterState.Sliding) {
                 charAnimation.CrossFade(slideAnimation.name);
             } else {
                 charAnimation.CrossFade(runAnimation.name);
             }
         }
     }
 
         void SyncRunAnimation() {
         Debug.Log("Sync Run");
         transform.position += new Vector3(0, 3, 0);
     }
 }

Before assigning the animation, the character is standing in the ground at position (0, 0.6, 0). After assigning, the character submerges INTO the ground, stuck; position changed to (0, -0.75, -0.55). How can I control the animation position ?

Note: I tried to use SyncEvent to move up ( increase Y axis ), but it does NO effect at all.

UPDATE This only happens when Animation is set to Legacy. If I set the animation to Generic, it has no problem, but Console issues errors :

The AnimationClip 'run' used by the Animation component 'MyCharacter' must be marked as Legacy.

and the animation could not be played. How can I make it work with Generic animation / correct position with Legacy animation ?

UPDATE 2 Here is a simplified version of the scene, WITHOUT any script.

Before I hit the "PLAY" button

After I hit the "PLAY" button

So the problem is not related to codes, right ?