plugin development - WordPress REST API call generates nonce twice on every call

I'm trying to login a user via the REST API, and then retrieve the current user on subsequent requests. As per the documentation, in my plugin, I am creating and retrieving a nonce after a successful login. The nonce is returned correctly, but every REST call results in a wp_create_nonce() call which resets the nonce, this is followed by another call to it with action = heartbeat-nonce call, which resets it again and then wp_create_nonce() is called again which resets it back. So after I login the user the nonce has changed.

Now when I make my next API call, the same thing happens again. This is results in any nonce I send with my API request invalid and current-user is set to 0 and thus my logged in user is never valid.

I tried creating a new nonce for every request, but the multiple calls to create_nonce, 3 every request, keeps resetting the nonce. I am logging calls to wp_create_nonce and I can see that even when I make no API calls, this function is called every 2 mins on it's own.

I am still working my way through the WordPress development, so please excuse any ignorance. I would really appreciate some help here as I can't seem to move past this point.

EDIT: Apologies for being unclear. I am working on a React front-end delivering WordPress content via the REST API. I am trying to authenticate a user, and then allow them to create a post. The user is an Author. To achieve this I made a plugin, that provides me routes to login, and then submit a post if the user is authorized.

register_rest_route($this->namespace, '/auth/login', array(
    'methods' => WP_REST_Server::CREATABLE,
    'callback' => array($this, 'reactpress_jwt_auth_user_signin'),
  ));

This eventually leads to the below function being called.

public static function reactpress_jwt_user_login($user_obj){

//Login user with wp_signon()
$credentials = array(
  'user_login' => $user_obj['username'],
  'user_password' => $user_obj['password'],
  'remember' => false
);

$user = wp_signon( $credentials, false );

if(!is_wp_error($user)){

  //Set the current user
  $current_user = wp_set_current_user($user->data->ID);

  //This calls wp_create_nonce('wp_rest');
  $nonce_val = self::reactpress_jwt_generate_nonce(); 

  $response = array(
    'user' => $current_user->data->user_nicename,
    'nonce' => $nonce_val
  );

  return $response;

}else{
  return new WP_Error('reactpress-jwt-auth-fail', 'User signin failed ' . $user->message);
}
}

Now when I make a second call to the API, I'm setting _wpnonce as this returned nonce value. But it never matches because the nonce value is regenerated by the 3 calls to wp_create_nonce(). I'm using Postman to send my requests.

I logged calls to wp_create_nonce and below is a sample from by debug.log, of the function being called automatically from somewhere, i.e. not after an explicit call to the REST API by me.

[16-Dec-2018 19:07:23 UTC] INSIDE CREATE NONCE wp_rest
[16-Dec-2018 19:07:23 UTC] CURRENT USER ID IS 1
[16-Dec-2018 19:07:23 UTC] GENERATED NONCE IS  8d7dd8f044
[16-Dec-2018 19:07:23 UTC] INSIDE CREATE NONCE heartbeat-nonce
[16-Dec-2018 19:07:23 UTC] CURRENT USER ID IS 1
[16-Dec-2018 19:07:23 UTC] GENERATED NONCE IS  c719f185fc
[16-Dec-2018 19:07:23 UTC] INSIDE CREATE NONCE updates
[16-Dec-2018 19:07:23 UTC] CURRENT USER ID IS 1
[16-Dec-2018 19:07:23 UTC] GENERATED NONCE IS  c1701a5519
[16-Dec-2018 19:07:23 UTC] INSIDE CREATE NONCE wp_rest
[16-Dec-2018 19:07:23 UTC] CURRENT USER ID IS 1
[16-Dec-2018 19:07:23 UTC] GENERATED NONCE IS  8d7dd8f044
[16-Dec-2018 19:07:23 UTC] Inside VERIFY NONCE c719f185fc
[16-Dec-2018 19:07:23 UTC] CURRENT USER ID  1
[16-Dec-2018 19:07:23 UTC] nonce generated 0-12 hours ago

The user I logged in has User id 2. I am logged into the backend via my Admin user, with User ID 1. Could that be what is causing this?

EDIT: No, logging in as Admin is not the cause. I tried again without logging into the backend. Received a nonce after logged in and placed a request.

[17-Dec-2018 06:59:37 UTC] INSIDE REST COOKIE CHECK ERRORS
[17-Dec-2018 06:59:37 UTC] _wpnonce is set 67c6049b8b
[17-Dec-2018 06:59:37 UTC] Inside VERIFY NONCE 67c6049b8b
[17-Dec-2018 06:59:37 UTC] CURRENT USER ID  2
[17-Dec-2018 06:59:37 UTC] nonce NOT generated 0-12 hours ago expected it to be --> add87a8b0b
[17-Dec-2018 06:59:37 UTC] nonce NOT generated 12-24 hours ago expected it to be --> 5523ad082e

67c6049b8b is the nonce I received after login, and which I sent with my second API call, which returned:

{
 "code": "rest_cookie_invalid_nonce",
 "message": "Cookie nonce is invalid",
 "data": {
    "status": 403
 }
}