ASP.NET Identity UpdateAsync returns 'Object not set to an instance of an object' after conversion from visual studio 2015 to 2017

Question

My ASP.NET identity UpdateAsync stopped working without any change in my code. I was working on this project with Visual studio 2015 but recently moved to 2017. I also changed from IIS express in visual to Full IIS. Everything works fine except updateAsync when updating user data.

It throws a silent error "Object not set to an instance of an object" when I call the user manager. The confusing part is that the same user manager is used to create a new user, get a collection of users etc. Only updateAsync fails. I just can get my head around what may be causing this behavior:

public class AppUser : IdentityUser<int, AppUserLogin, AppUserRole, AppUserClaim>, IUser<int>
{
    [Index("EmployeeNumberIndex",IsUnique = true)]
    public int EmployeeNumber { set; get; }

    public virtual string FirstName { set; get; }

    public virtual string MiddleName { set; get; }

    public virtual string LastName { set; get; }

    public virtual string Sex { set; get; }

    public virtual DateTime DateOfBirth { set; get; }

    public virtual int UserType { set; get; }  // 0 for normall memebers and 1 for admin

    public virtual DateTime DateJoined { set; get; }

    public virtual string ProfileImage { set; get; }

    public virtual string DepartmentName { set; get; }

    public virtual string Jobdescription { set; get; }

    public virtual string Password { set; get; }

    public virtual int PasswordChanged { set; get; }

    // guarantors details
    public virtual string Guarantor1FullName { set; get; }
    public virtual string Guarantor1Address { set; get; }
    public virtual string Guarantor1PhoneNumber { set; get; }
    public virtual string Guarantor1Email { set; get; }

    public virtual string Guarantor2FullName { set; get; }
    public virtual string Guarantor2Address { set; get; }
    public virtual string Guarantor2PhoneNumber { set; get; }
    public virtual string Guarantor2Email { set; get; }




    public async Task<ClaimsIdentity> GenerateUserIdentityAsync(AppUserManager manager, string authenticationType)
    {
        var userIdentity = await manager.CreateIdentityAsync(this, authenticationType);
        // Add custom user claims here
        return userIdentity;
    }

}

This is the method that calls the updateAsync

public async Task<IdentityResult> UpdateUser(AppUser user)
    {
        AppUser usr;
        usr = await UserManager().FindByIdAsync(user.Id);
        if (usr == null)
        {
            return new IdentityResult("Member does not exist!");
        }

        usr.EmployeeNumber = user.EmployeeNumber;
        usr.FirstName = user.FirstName;
        usr.LastName = user.LastName;
        usr.MiddleName = user.MiddleName;
        usr.PhoneNumber = user.PhoneNumber;
        usr.Email = user.Email;
        usr.UserName = user.Email;
        usr.ProfileImage = user.ProfileImage;
        usr.Jobdescription = user.Jobdescription;

        if (user.DateJoined != DateTime.MinValue)  
        {
            usr.DateJoined = user.DateJoined;
        }

        if (user.DateOfBirth != DateTime.MinValue)
        {
            usr.DateOfBirth = user.DateOfBirth;
        }

        if (user.Sex != null)
        {
            usr.Sex = user.Sex;
        }

        usr.Guarantor1Address = user.Guarantor1Address;
        usr.Guarantor1Email = user.Guarantor1Email;
        usr.Guarantor1FullName = user.Guarantor1FullName;
        usr.Guarantor1PhoneNumber = user.Guarantor2PhoneNumber;
        usr.Guarantor2Address = user.Guarantor2Address;
        usr.Guarantor2Email = user.Guarantor2Email;
        usr.Guarantor2FullName = user.Guarantor2FullName;
        usr.Guarantor2PhoneNumber = user.Guarantor2PhoneNumber;


        try
        {
            return await UserManager().UpdateAsync(usr);

        }catch(Exception ex)
        {
            throw ex;
        }


    }

This the line that fails without inner exception:

return await UserManager().UpdateAsync(usr);

This is the UserManager

    public AppUserManager UserManager()
    {
       return HttpContext.Current.GetOwinContext().GetUserManager<AppUserManager>();

    }

While this is the appUserManager:

public class AppUserManager : UserManager<AppUser, int>
{
    public AppUserManager(IUserStore<AppUser, int> store)
        : base(store)
    {

    }

    public static AppUserManager Create(IdentityFactoryOptions<AppUserManager> options, IOwinContext context)
    {

        AppIdentityDbContext db = context.Get<AppIdentityDbContext>();
        AppUserManager manager = new AppUserManager(new AppUserStore(db));


        // add password validations
        manager.PasswordValidator = new CustomPasswordValidator()
        {
            RequiredLength = 8,
            RequireNonLetterOrDigit = true,
            RequireUppercase = true,
            RequireDigit = true,
            RequireLowercase=true

        };


        manager.UserValidator = new UserValidator<AppUser, int>(manager)
        {
            RequireUniqueEmail = true,

        };

        var provider = new DpapiDataProtectionProvider("http://coopone.local");
        manager.UserTokenProvider =
            new DataProtectorTokenProvider<AppUser, int>(provider.Create("Email Reset"));
        ;

        return manager;
    }
}