Async Await in asp.net core web api?

Question

On first request method gets executed but on the second call it doesn't, I am aslo using await keyword?

 

The method which I am calling is not an async method?

 

When I debug the code user comes null once I logout and again login but by going inside the method with F11 user gets filled, can someone help me to understand this?

public async Task<IActionResult> AuthenticateUser([FromBody] User user)
{
Login login = new Login();
user = await login.AuthenticateUser(user.LoginId, user.Password);
if (userDetails!=null)
{
return Ok(userDetails);
}
return BadRequest();
}