I think you'll find that mashing on play or pause buttons for audio with even hand-coded audio will crash iBooks. I've been troubleshooting iBooks widgets for years now and audio remains one of the most finicky and troublesome issues in iBooks. Apple has a challenge where they need to make sure that the full spectrum of web technologies are supported within the widget area, while at the same time making sure that there is enough memory left over for the actual book itself which is running underneath the widget when a widget is opened.
Apple has both a timer and a likely protection mechanism that flushes widgets from memory if they continue to run in the back ground. This is not something we have any transparency over -- we can't ask Apple 'why did you close the widget?' or 'what is the memory limit for a widget?'
It's simply not information that provide in any of their developer documentation.
You can see all the information Apple has volunteered here: https://support.apple.com/en-us/HT204433. Keep in mind that widgets must play on iPads that are over 6 years old.
If you disregard all of these reasons, the real thing you should know about Hype and these forums is that you'll get much more accurate help if you can share your Hype document, and even more help if you approach issues with patience and the members of this forum with kindness.