Chrome only: interactive book plays audio in next chapter

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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.

Same goes for when I get to the third chapter. Audio from the fourth chapter starts playing simultaneously. Etc.

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.