I’m afraid you’re going to need to give us more to go on.
Are you getting errors? Are things not working as you expect? What EXACTLY is going on?
In linked indesign file example, in page 4, exercise 5 the MSO doesn't work.
The image bellow shows exercise 5, when I choose letter C (wrong option), I can't choose letter B or A, even the buttons and actions are done in MSO.
The same quiz model in pages 2 and 3 works well.
Any idea why MSO in ePUB get unstable?
Your link is broken.
Your link is still broken.
I guess you missed a part of it while copy it over to your message.
This time I could download the samples.
I can confirm your issues.
It seems everything is alright with the targets of the buttons.
They are defined in the right way.
Maybe they are nested too deep in several groups?
The two buttons are grouped inside a group.
To be precise, the outer group has one single object: A group that consists of two buttons.
Maybe that's the whole problem? Do you remember how you did accomplish this?
I reworked that state by ungrouping everything, all two buttons are now first level object in that state.
Then I had to reassign the targets (goToState actions), because my ungouping stripped off all the gotToState actions (a bug).
After that the MSO was working as expected.