Jumping is randomly not working.

Hello,

I am new to Unity and just tried to make a little platformer. Most of the time it works fine, but sometimes the jump just won't work for a couple of seconds. I have no idea why that happens and I hope someone can maybe help me.

Thanks a lot!

This is my code for jumping:

 [Range(1, 10)]
 public float jumpVelocity;

 public float fallMultiplier = 2.5f;
 public float lowJumpMultiplier = 2f;
 public LayerMask groundLayer;
 Rigidbody2D rb;

 bool IsGrounded()
 {
     Vector2 position = transform.position;
     Vector2 direction = Vector2.down;
     float distance = 0.7f;

     RaycastHit2D hit = Physics2D.Raycast(position, direction, distance, groundLayer);
     if (hit.collider != null)
     {
         return true;
     }
     else
     {
         return false;
     }
 }
 
 void Awake () {
     rb = GetComponent<Rigidbody2D>();
 }
 
 void FixedUpdate () {

     if (Input.GetButtonDown("Jump"))
     {
         Jumpnow();
     }

     //Add better jumping
     if (rb.velocity.y < 0)
     {
         rb.velocity += Vector2.up * Physics2D.gravity.y * (fallMultiplier - 1) * Time.deltaTime;
     }
     else if(rb.velocity.y > 0 && !Input.GetButton("Jump")){
         rb.velocity += Vector2.up * Physics2D.gravity.y * (lowJumpMultiplier - 1) * Time.deltaTime; 
     }
 }
 void Jumpnow()
 {
     if (!IsGrounded())
     {
         return;
     }
     else
     {
         rb.velocity = Vector2.up * jumpVelocity;
     }
 }