Cached values returned after TransactionScope.Dispose()

I'm a newbie in integration tests and I'm looking for some explanation and advice about workaround of my issue:

I'm using TransactionScope in my tests to keep database clean and creating new TransactionScope before each test and dispose it after each test:

 [SetUp]
    public void Init()
    {
        this.scope = new TransactionScope(
            TransactionScopeOption.Required,
            new TransactionOptions() { IsolationLevel = IsolationLevel.ReadUncommitted },
            TransactionScopeAsyncFlowOption.Enabled);
        this.context = new SportsPerformanceDbContext();
        this.questRepo = new QuestionRepository(this.context);
    }

    [TearDown]
    public void CleanAll()
    {
        this.context.Dispose();
        this.scope.Dispose();
    }

Everything works ok when I run one test class. But when I run at least two test classes, I'm facing a problem: in this test (see below) lasrQuestionId equals the last question id from database - that's ok, but actualResultId equals the Id_of_the_last_added_question_in_tests_with_transaction_scope + 1:

[Test]
    public async void AddAsyncTest()
    {
        // Arrange
        var questionModel = new QuestionModel
        {
            //some properties
        };
        Question lastQuestion = this.GetLastQuestion();
        var lastQuestionId = lastQuestion?.Id ?? 0;

        // Act
        var addResult = await this.questRepo.AddAsync(questionModel);
        var actualResult = addResult.Value;

        // Assert
        Assert.AreEqual(lastQuestionId + 1, actualResult.Id);
        // some other assertions
    }

So I have the following, e.g., lastQuestionId is 5 (5 questions in Database), but actualResult Id is 16 (because I've previously added some questions in other tests)... I assume that there is a problem with my context or scope.dispose(). I don't know where is a problem, could you explain what am I doing wrong here? Thanks in advance!

this.GetLastQuestion() code is below:

 private Question GetLastQuestion()
    {
        using (var ctx = new SportsPerformanceDbContext())
        {
            return ctx.Question
             .OrderByDescending(q => q.Id)
             .FirstOrDefault();
        }
    }