title: Entity Framework core Include() is not working after upgrading from version 3.1.2 to 5.0.3
body: <p>I have a project that was running with .net core 3.1. After upgrading to .net 5 and entity framework core to 5.0.3, the include is not working anymore.</p>
  <p>I have these classes</p>
  <pre class="lang-cs prettyprint-override"><code>public class Question
  {
      [Key]
      public Guid Id { get; set; }
      public string QuestionCode { get; set; }
      [ForeignKey(&quot;AnswersId&quot;)]
      public Answer Answers { get; set; }
  }
  
  public class Answer
  {
      [Key]
      public Guid Id { get; set; }
      public string Answers { get; set; }
      public int Score { get; set; }
  }
  </code></pre>
  <p>The relation is defined as follows:</p>
  <pre class="lang-cs prettyprint-override"><code>protected override void OnModelCreating(ModelBuilder modelBuilder)
  {
      modelBuilder.Entity&lt;Question&gt;()
          .HasOne(q =&gt; q.Answers);
  }
  </code></pre>
  <p>and this simple LINQ:</p>
  <pre class="lang-cs prettyprint-override"><code>return _context.Questions
          .Include(q =&gt; q.Answers)
          .FirstOrDefault(s =&gt; s.Id == id);
  </code></pre>
  <p>however. the include is not working after the version upgrade. By not working i mean the returned values doesn't include Answers. Main entity only is returned and all the fields in the child are null.</p>