EFCore DbContext showing different results despite having SavedChanges

I am struggling with EF Core in my MVC.NET Core project.

I have 2 classes that represent 2 tables in the database. An Owner and an Address, with a classic one to many relationship. In this situation, one owner can have many addresses but each address can only have 1 owner.

When I run the code below, no exceptions are thrown (other than the Assert).

var entity = new Entities();
entity.Database.EnsureDeleted();
entity.Database.EnsureCreated();

var owner = new Owner()
{
    Name = "Claire"
}

entity.Owner.Add(owner);
entity.SaveChanges();

var address = new Address()
{
    Street = "10 My Road",                
    Owner = owner //get the only owner from the database
};           

entity.Address.Add(address);
entity.SaveChanges();  //After save changes, if I check the `entity` object, I can see the `Owner` has a child of `Address` as expected.


//now re-test to make sure it's right
var ent = new Entities();
Assert.That(entity.Addresses.Count() == ent.Addresses.Count());  //This passes
Assert.That(entity.Owner.Single().Addresses.Count() == ent.Owner.Single().Addresses.Count()); //this fails

When I inspect the ent.Addresses object, I can see the Owner property is null. This is where the fault is but I don't understand why it's null.

My objects that represent the tables are very simple

[Table("Owner")]
internal class Owner
{
    public Owner()
    {
        Addresses = new HashSet<Address>();
    }

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

    public int Id { get; set; }

    public string Name { get; set; }

    public virtual ICollection<Address> Addresses { get; set; }

and

[Table("Address")]
internal class Address
{
    public string Street { get; set; }
    public virtual Owner Owner { get; set; }
}

And finally by DBContext class is

internal class Entities : DbContext
{
    public DbSet<Owner> Owners{ get; set; }

    public DbSet<Address> Addresses { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        var contextFactory = new ContextFactory();
        contextFactory.Configure(optionsBuilder);
    }
}

I only have 1 appsettings.json file with a single connection string in my application which is set to always copy to output directly!

A break point in the code where I recreate the database confirms it's only being recreated at start up!

My understanding is, that despite having 2 DBContext objects, everything should still work because I am saving the data to the database and then querying direct from the database.

Why is this happening?