Hello @VanessaCouzens ...
It sounds like you are using current Classic Quizzes. In my own testing of a quiz in my sandbox course, if I have instructions for a Classic Quiz and have it set to display one question at a time, then it does show those instructions at the top of every question. However, if I build a New Quiz with instructions and also set the New Quiz to display one question at a time, when I preview that quiz, the instructions are only displaying above Question #1. When I move on to Question #2, the instructions go away. Here are a couple screenshots from my own sandbox course for a New Quiz:
Question 1 with instructions displayed
Question 2 with no instructions displayed
Hope this will help a bit. Let Community members know if you have any other questions about this...thanks!