To reproduce:

1. create 6 questions no matter of what type, in my case 5 copies of an essay questions
2. create a quiz
3. add an section heading
4. add two of the 6 questions
5. add another section heading
6. add another two questions
7. click on the "add" after the first question of the test and choose "from question bank"
8. add one of the unused questions 
9. the result is that the question is added at the end of the test and not after question 1

And shouldn't there be another "add"-link after question 2 of section 1?

I tested that on Moodle3.4 and in a free moodlecloud.com site.