When setting up your Debrief Exercise, the questions should match the questions in the dependent exercise.
If they do not, you will get a configuration warning similar to below:
The Solution
You will need to access the Debrief Exercise set up > untick Auto Assign Questions > Save > scroll down to view the question tree and remove (or add depending on the warning) the questions that do not match the dependent exercise.
Additional note - The Debrief Exercise can only have ONE dependent exercise.