How do you allow free navigation across all quiz slides?

I've been working in SL for so long that I've forgotten (or can't find) how to do certain things in Studio/QM anymore - and this seems to be one of them.

I have a course with something like 50 slides.  There are maybe 10 quiz slides dotted around and a final assessment at the end.  How do I enable the learner to use the player buttons (back/next) to move away from those initial quiz slides without getting the "Notification ... You must complete these questions in order to continue." each time they return to it even if they've competed it?  This stops them going back to the previous slide, so they then have to click "Finish" (even though they completed the quiz on an earlier attempt) just to get to the next slide when they can then use the side menu to go back to the previous chapter before having to move forward to the slide before the quiz.  Does that make sense?

The learner must be able to visit any part of the course at any time, so I've played with settings like:

- allow user to leave quiz = at any time

- may view slides after quiz = at any time

- may attempt quiz = unlimited times

I've tried every setting combination possible but can't get it to work.  Hands up if I'm being stupid

Any ideas?

Thanks

Simon