Are there suggestions for places to look when an app keeps closing?

We have an app that is being created that is using Bloom books as it’s source. The first book in the app works. We can advance from page to page and play the audio. We can advance the pages on the second and third book as well, but the app quits when we attempt to play audio. This has occurred on two different phones.

Any troubleshooting ideas?

As best as we can tell, the failure was because the audio files were named with numbers only (1.mp3, 2.mp3, 3.mp3 and so forth)
I added some text in front of the number and now it plays.

Sounds like a bug to me.