Question Bank Issue

I have included 50 questions in a question bank in SL2 (update 5). 25 questions are randomly drawn every time a user takes the course.The questions are of two types only : True / False  and Multiple Choice.All questions are set to draw randomly.

I have set the attempts to unlimited and feedback to none.Deleted the correct / incorrect layer prompt from every question.The interaction will be submitted when a user will click either previous or next button.Not the submit button.

The issue i'm facing is that, if i try to go back to a previously answered question to select a new answer, it's taking me to a new question.

I have tried all possible settings in Question Bank to lock questions below, to draw it always, etc.

Can i set-up 25 questions out of 50 to be drawn randomly every time other than the Question Bank?

Please provide me with a workaround or solution to this.

Thanks in advance.