Character Controller .isGrounded=false while moving left or right

I am making a 2D game. I have a character controller with gravity. When the controller is grounded isGrounded=true. But when the character is grounded and the character is moving left or right isGrounded=false.

 using UnityEngine;
 using System.Collections;
 
 public class PlayerC: MonoBehaviour {
     
     
 private CharacterController controller;
     
 // Use this for initialization
 void Start () {
 controller = GetComponent<CharacterController>();
 }
     
 // Update is called once per frame
 void Update () {
         
 
 //left / right
 if(Input.GetAxis("Horizontal") > 0)
 {
 
     controller.Move(Vector3.right * Input.GetAxis("Horizontal") * Time.deltaTime);
         }
         else if(Input.GetAxis("Horizontal") < 0)
         {
 
             controller.Move(Vector3.right * Input.GetAxis("Horizontal") * Time.deltaTime);
         }
 
         print (controller.isGrounded);
         
         //jump
         if(Input.GetButton("Jump") && controller.isGrounded)
         {
             controller.Move (Vector3.up * 10 * Time.deltaTime);
         }
         
         //gravity
         controller.Move (Vector3.down*2 * Time.deltaTime);
         
     }
     
 }

I can not figure out why isGrounded is becoming false when I am using controller.Move. It is a very annoying problem.