Chrome only: interactive book plays audio in next chapter

I'm using an interactive book widget in Moodle 3.9 to play sections of a SCORM course by using iframe embedders to embed each section in a chapter of the interactive book.

But ON CHROME ONLY, when I load the first chapter, the audio/video for the second chapter loads and starts playing simultaneously with the first, causing distracting audio overlap.

I looked at the code for the interactive book widget, where in the file pagecontent.js there is a two-line method "preloadChapter" whose function is to "Preload current chapter and the next one" according to the comment.

I deleted the second line of the method,  thinking that only the current chapter would then be preloaded.  But to my surprise, deleting the line had no effect.

Can I get some hints as to why only Chrome shows this behavior and how to stop content from the next chapter from playing when the current chapter starts?  My course would be student-ready if it weren't for this issue.