HttpContext.SignOutAsync() neither logs out the user nor deletes the local cookie

I know there are already questions about this topic but none of the given answers worked in my situation.

Here's the core:

Startup.cs

public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<comedyContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

        services.Configure<CookiePolicyOptions>(options =>
        {
            // This lambda determines whether user consent for non-essential cookies is needed for a given request.
            options.CheckConsentNeeded = context => true;
            options.MinimumSameSitePolicy = SameSiteMode.None;
        });

        services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
            .AddCookie(options => {
                options.LoginPath = "/login/";
            });

        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Error");
            // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }

        app.UseHttpsRedirection();
        app.UseStaticFiles();
        app.UseCookiePolicy();
        app.UseAuthentication();

        app.UseMvc();
    }

Login.cshtml.cs

    public class LoginModel : PageModel
{
    [BindProperty]
    public string inputUsername { get; set; }
    [BindProperty]
    public string inputPassword { get; set; }

    private readonly comedyContext _context;

    public LoginModel(comedyContext context)
    {
        _context = context;
    }

    public async Task<IActionResult> OnPostAsync()
    {
        var user = await _context.User.FirstOrDefaultAsync(u =>
            string.Equals(u.Username, inputUsername, StringComparison.CurrentCultureIgnoreCase) && string.Equals(u.Password, Utility.sha256_hash(inputPassword), StringComparison.CurrentCultureIgnoreCase));

        if (user is null)
            return Redirect("/login");

        var claims = new List<Claim>
        {
            new Claim(ClaimTypes.NameIdentifier, user.UserId.ToString()),
            new Claim(ClaimTypes.Name, inputUsername)
        };

        var userIdentity = new ClaimsIdentity(claims, CookieAuthenticationDefaults.AuthenticationScheme);

        var authProperties = new AuthenticationProperties
        {
            AllowRefresh = true,
            // Refreshing the authentication session should be allowed.

            ExpiresUtc = DateTimeOffset.UtcNow.AddHours(24),
            // The time at which the authentication ticket expires. A 
            // value set here overrides the ExpireTimeSpan option of 
            // CookieAuthenticationOptions set with AddCookie.

            IsPersistent = true,
            // Whether the authentication session is persisted across 
            // multiple requests. Required when setting the 
            // ExpireTimeSpan option of CookieAuthenticationOptions 
            // set with AddCookie. Also required when setting 
            // ExpiresUtc.

            IssuedUtc = DateTimeOffset.UtcNow,
            // The time at which the authentication ticket was issued.

            //RedirectUri = <string>
            // The full path or absolute URI to be used as an http 
            // redirect response value.
        };

        await HttpContext.SignInAsync(CookieAuthenticationDefaults.AuthenticationScheme, new ClaimsPrincipal(userIdentity), authProperties);

        //Just redirect to our index after logging in. 
        return Redirect("/dashboard");
    }

    public void OnGet()
    {
    }
}

Dashboard.cshtml

@page
@using System.Security.Claims
@using Microsoft.AspNetCore.Identity
@using ComedyWebsite.Controllers
@model ComedyWebsite.Pages.DashboardModel
@{
}

Hello @User.Claims.FirstOrDefault(c => c.Type == ClaimTypes.Name)?.Value

<form asp-controller="Logout" asp-action="Logout" method="post" 
id="logoutForm">
    <button type="submit">Logout</button>
</form>

LogoutController.cs

public class LogoutController : Controller
{
    [HttpPost]
    public async Task<IActionResult> Logout()
    {
        // SomeOtherPage is where we redirect to after signout
        await HttpContext.SignOutAsync(CookieAuthenticationDefaults.AuthenticationScheme);
        HttpContext.Response.Cookies.Delete($".AspNetCore.{CookieAuthenticationDefaults.AuthenticationScheme}");
        return Redirect("/");
    }
}

As the image below shows, after clicking the Logout button the cookie still exists in the user's browser

I tried the solution given here at https://stackoverflow.com/questions/46131517/asp-net-core-identity-2-0-signoutasync but that didn't work either.