AspNet-Contrib only works on a new project

Question

I have a ready-made project, and in it, when connecting authentication via Google, the connection does not work. All the standard settings described in the example. But if I create a new project, then everything works for me. What could be the problem? I can provide the necessary code

UPD

AccountController.cs

public async Task<IActionResult> SignIn(string provider)
    {
        return Challenge(new AuthenticationProperties { RedirectUri = "/Register" }, provider);
    }

And Startup.cs

services.AddAuthentication(options =>
        {
            options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
        })
        .AddCookie(options =>
        {
            options.LoginPath = "/signin";
            options.LogoutPath = "/signout";
        })
        .AddGoogle(options =>
        {
            options.ClientId = "myId";
            options.ClientSecret = "MySecret";
        });

I found a problem, if you finish this code then authorization does not occur

services.AddDbContext<MainContext>(options => 
options.UseSqlServer(_configuration.GetConnectionString("MainConnection")),
                ServiceLifetime.Transient);
        services.AddIdentity<User, Role>()
                 .AddEntityFrameworkStores<MainContext>()
                 .AddDefaultTokenProviders();