Glad to say I have finished an entire e-course and everything works fine.
In the end I have a quiz and the button "retake quiz" works fine as well.
But my "restart course" button although it works fine when clicked(really restarts the whole course and goes to the first slide). After a couple slides when some "chose the right answer out of many" questions start (prior the quiz) I cannot click the choices.
Why is this happening?
edit* for me this is happening both in preview and published versions of my course.