ASP.NET MVC Not logged in successfully showing 404 error - asp.net-mvc

Question

I have a ASP.NET MVC app running with Forms Authenticated enabled.
In my own machine and browser (Edge,IE,chrome), I am able to login in my website.
It works for other users as well. But, for some users, they are not able to login to the home page of the website and it is going to 404 page not found error....
I am sharing my code behind..
Login action method
[HttpPost]
[AllowAnonymous]
public ActionResult LoginUser(LoginUser login)
{
if (ModelState.IsValid)
{
if(AuthenticateUserAD(login) != "")
{
FormsAuthentication.SetAuthCookie(login.UserName, login.RememberMe);
if (login.RememberMe)
{
HttpCookie cookie = new HttpCookie("Login");
cookie.Values.Add("UserName", login.UserName);
cookie.Values.Add("Password", login.Password);
cookie.Expires = DateTime.Now.AddDays(10);
Response.Cookies.Add(cookie);
}
ViewBag.IsLoginValid = "Valid";
return RedirectToAction("Index", "Service");
}
else
{
ViewBag.Invalid = Session["error"].ToString();
ViewBag.IsLoginValid = "Invalid";
return View("LoginUser");
}
}
else
{
ModelState.AddModelError("", "The user name or password provided is incorrect");
}
return View(login);
}
LoginUser.cshtml
#using (Html.BeginForm("LoginUser", null, FormMethod.Post))
{
<div class="row mt-5">
<div class="col-6 col-sm-6 offset-3 bodyColor" style="border-radius: 25px;">
<div class="col-8 col-sm-8 offset-2">
<div style="max-width: 400px;">
<div class="text-center section-title">
<h2>Login</h2>
</div>
#Html.LabelFor(model => model.UserName)
<div class="input-group form-group">
<div class="input-group-prepend">
<span class="input-group-text date-Textbox"><i class="fa fa-user"></i></span>
</div>
#Html.TextBoxFor(model => model.UserName, new { #class = "form-control textbox-font" })
#Html.ValidationMessageFor(model => model.UserName, "", new { #class = "textRed" })
</div>
#Html.LabelFor(model => model.Password)
<div class="input-group form-group">
<div class="input-group-prepend">
<span class="input-group-text date-Textbox"><i class="fa fa-lock"></i></span>
</div>
#Html.TextBoxFor(model => model.Password, new { #class = "form-control textbox-font", type = "password" })
#Html.ValidationMessageFor(model => model.Password, "", new { #class = "textRed" })
</div>
#Html.CheckBoxFor(model => model.RememberMe)
#Html.LabelFor(model => model.RememberMe)
<input type="hidden" name="ReturnUrl" value="#Request.QueryString["ReturnUrl"]" />
<div class="col-sm-12 col-xs-12">
<input type="submit" value="Login" id="btnLogin" style="width:100%;" autofocus class="btn btn-main-custom" />
</div>
</div>
</div>
}
I really do not know whether this is a browser problem or a development problem or cookies problem.
Appreciate any help, Could anyone find a solution or a workaround?
Thanks