Loading related data does not work, how to solve?

Question

C++ / C#

I have code

// подключил
using IslandCity.Models;
using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using IslandCity.App_Data;
using Microsoft.AspNetCore.Http;
using Newtonsoft.Json;
using Microsoft.EntityFrameworkCore;


User user = db.Users
                .Include(context => context.Lands)
                     .ThenInclude(land => land.Card)
                .Include(context => context.Cards)
                .FirstOrDefault(u => u.Name == accountName);

but land.Card == null although it shouldn't,

why and how to fix it?
I will be grateful for any answer!