That's really the main problem. You're building your foundation on sand. Unfortunately, iBooks Author is dead tech. Apple isn't supporting it anymore. They took it off the app store. The original version of A Book About Hype was an iBook. I wanted to create something interactive, to showcase what could be built with Hype. But even under ideal conditions, it meant only targeting Apple devices. Many other ePub readers don't support Apple's iBooks widgets. Even on iPad or iPhone, if you flipped through the pages too quickly, the book could crash.
For the next edition of the book, I created a printed book. I went back to paper... PAPER! It's because Apple just abandoned this tech.
But, even if you were to convert your Hype project to an app, it looks like this might still be an issue. You mentioned it's slow in Hype Reflect too. That's a problem? How do you fix it?
I don't know. I haven't seen your project. But if I was working on a project with this problem, I'd probably use the developer tools to determine what's causing the project to slow down.
This is why I like Safari. It has developer tools that work with iOS devices. First, you'll need the developer tools turned on. (That's a setting in Safari Preferences.) Then, launch your Hype project in a web browser. You can accomplish this by putting it on your own web server or pressing the Safari icon when using Hype reflect.
Once it's running in the browser on the iOS device, launch the dev tools from Mac Safari.
From there, you can use the tools to get a closer look at what's going on.
Are there any errors in the console? Is there too much memory being used? What exactly is slowing down... and when does that slowdown occur. The first step in solving this problem is identifying exactly what's wrong. The developer tools might help you.