IIS web requests are hanging indefinitely - OWIN module

Question

A web app (ASP .NET MVC - C#) works on a windows machine and it is hosted already on IIS 8.5. The app uses Membership along with .NET framework 4.5.

Recently, it went down twice upon the total response time reached more than 1 million milliseconds.

I have checked the IIS Worker Process and I saw all requests are stuck there as per the below screenshot in PreExecuteRequestHeaders in OWIN module, the application has no changes since too long time ago, and the traffic is not high.

I can see there is another question which had the same issue, but the problem here I wanna know why or what is the root cause of the issue? Because, I am not using async calls in this application.

EDIT: I am using the blow in the startup:

[assembly: OwinStartupAttribute(typeof(MyProject.Startup))]
namespace MyProject
{
    public partial class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            // some other configurations which are related to logs ... bla bla bla
        }
    }
}

public partial class Startup
{
    // For more information on configuring authentication, please visit http://go.microsoft.com/fwlink/?LinkId=301864
    public void ConfigureAuth(IAppBuilder app)
    {
        // Enable the application to use a cookie to store information for the signed in user
        app.UseCookieAuthentication(new CookieAuthenticationOptions
        {
            AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
            LoginPath = new PathString("/Account/Login")
        });
        // Use a cookie to temporarily store information about a user logging in with a third party login provider
        app.UseExternalSignInCookie(DefaultAuthenticationTypes.ExternalCookie);
    }
}