The related table couldn't be load with other related table

Question

I have problem with a related tables in SQLite database. Database create by code (CodeFirst). And I using EFCore for working with database.

I have next classes (Please, have attention to the Client property):

public partial class Firmwares
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Key]
    public int Id { get; set; }

    public int ControlBlockTypesId { get; set; }
    public ControlBlockTypes ControlBlockType { get; set; }

    public int ControlBlockProducersId { get; set; }
    public ControlBlockProducers ControlBlockProducer { get; set; }

    public int CategoriesId { get; set; }
    public Categories Category { get; set; }

    public string SerialNumber { get; set; }

    public string Hardware { get; set; }

    public string Software { get; set; }

    public DateTime CreateDate { get; set; }

    public int ClientsId { get; set; }
    public Clients Client { get; set; }

    public string FileName { get; set; }

    public string Comment { get; set; }
}

public class Clients
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Key]
    public int Id { get; set; }
    public string FullName { get; set; }
    public string PhoneNumber { get; set; }
    public DateTime YearOfCar { get; set; }
    public string VINCode { get; set; }
    public ICollection<Firmwares> Firmware { get; set; }
}

And next model creator (removed other table creators):

protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Clients>().ToTable("Clients");
        modelBuilder.Entity<Firmwares>().ToTable("Firmwares");
    }

And when I try get list of Firmwares, there is Client equal null.

I tried to change declaration of ForeignKeys (by the attribute in the class, in the ModelBuilder and how it in code). But it didn't help.

How I get the list of Firmwares:

        IQueryable<Firmwares> searchingFirmwares;
        switch (SearchingParametr)
        {
            case "Search.ClientPhone": { searchingFirmwares = MainWindow.Database.Firmwares.Where(w => w.Client.PhoneNumber.Contains(Text)); break; }
            default: { searchingFirmwares = MainWindow.Database.Firmwares; break; }
        }

        SearchingFirmwares = searchingFirmwares.Include(w=>w.Client).ToList();

I read that it can be a Lazy Loading. But Include method didn't helped too.

But when I drop the database, create again and fill it with a test data, it's work - the Client isn't empty. After rebooting application, Client is empty again.

Can anybody help me with this problem? Maybe some advices? Some other ways to try?