First-time ePub 3 is unstable when put to the test, Please help

I have recently designed my very first ebook - an ePub3 with InDesign CC 2018. I wanted to design a multi-chapter book with reflowable text, a few images and audio files. I learned how to do this from online tutorials. Now after testing on different devices and readers, I feel like my finished book is not 100% stable.

Here is the basic specs of my project files:

- reflowable .epub

- 3 audio file links

- 1 animated .gif

- multiple images

The set up of my project file is multiple InDesign documents in a book project. Each chapter as well as About The Author, Book Credits and Title Page are each their own InDesign document. I did this because my chapter titles are custom graphics and I wanted the e-reader to create TOC navigation based on file names since chapter titles use images instead of unique paragraph styles.

Also, i am not knowledgeable in html or CSS, so my layout appearance is all based purely on Object Export Options. (not sure if that matters)

The .epub works fine in iBooks on all of my Apple devices - iMac, iPhone and iPad. (However I did ecounter an issue where my exported .epub's were not displaying the audio players on just the iPad. I searched the forums and found a suggestion to revert back to InDesign CC and save files to legacy. After importing the legacy files to my InDesign book project, the audio files now work on the iPad). My issue now is that when testing on Android devices using Google Playbooks, the audio players don't show up at all and my .gif is no longer animated. I tried to export to ePub 2 to see if that might fix the problem, but got the message that the file was corrupted or unsupported by Google Play. The ePub 2 file was also a problem for Adobe Digital Editions - the display was all messed up with individual graphics being stretched across the whole screen. I anticipate that most of the consumers of this book will be mobile on either smartphone or tablet. I would prefer Android and Google Play users have the same experience as Apple users. I have searched and not found much info on this, but this is also my first experience with ePub so I don't know all the in's and out's of the ebook world. Any help is much appreciated as to how I can fix this audio and .gif issue, but if anyone is willing to take a look at my set-up that would be awesome! I have .zip folder with InDesign Project and .epub export I can share from Google Drive.