如果在ASP.NET Core Identity中使用自定义登录页面时遇到此问题，则需要在Startup.cs文件中的ConfigureServices方法中添加以下依赖注入服务代码：

services.AddRazorPages().AddRazorPagesOptions(options =>
{
    options.Conventions.AuthorizeAreaPage("Identity", "/Account/Logout");
    options.Conventions.AuthorizeAreaPage("Identity", "/Account/Manage/Index");
    options.Conventions.AuthorizeAreaPage("Identity", "/Account/Manage/ChangePassword");
    options.Conventions.AuthorizeAreaPage("Identity", "/Account/Manage/SetPassword");
    options.Conventions.AllowAnonymousToAreaPage("Identity", "/Account/Login");
    options.Conventions.AllowAnonymousToAreaPage("Identity", "/Account/Register");
}).AddSignInManager>();

此外，请确保您在登录页面.cshtml文件中的Page指令中包含@model WebApp.Areas.Identity.Pages.Account.LoginModel，例如：

@page
@model WebApp.Areas.Identity.Pages.Account.LoginModel