Resume the slide audio after having used the "stop slide audio" option of a button

Unless I misunderstand your question, I may have a solution in this video here: https://youtu.be/ojWz2spuTeM

If you want the slide audio to continue when you continue the timeline I would suggest NOT selecting the option to Stop Slide Audio.  Just use a Pause timeline action.  As Lieve said, the slide audio is synched with the timeline.  Stopping and starting the timeline should also just stop and start the slide audio.  I think the Stop Slide Audio option is intended to allow a user interaction on a button to turn off the slide audio even though the timeline continues playing.  The button might be invoking a Play Audio action.  The Stop Triggered Audio action does not affect Slide Audio, so you have to use the Stop Slide Audio option for the Action.

If only the Adobe Engineers had thought of including a Stop Slide Audio action to complement the Stop Triggered Audio action, and a Resume Slide Audio action to complement the Play Audio action.  Then you would have the ability to control both at will from Advanced Actions.

That is strange, because the audio is syncrhonized with the timeline and should restart aftet the pause. Can you tell what the action is on the close  button? And verify the exact version numer under Help, About Captivate?

Have a look at:

https://elearning.adobe.com/2018/06/pausing-timeline-audio-clips/