iOS app erratically freezing up when loading audio files

[Andreas Bergendal]

Hi folks,

I really need your help now. I’m developing a simple app for a client, to be run on iPads in an exhibition starting 8th Oct. It consists of two cards: 
a gallery card, with 16 photos
a profile card which you go to by clicking a photo on the gallery card

On the profile card this is loaded:
the photo again, larger
a short text in a field
an audio file (mp3), which starts playing

All resources are included in file folders with the app, no internet needed. The audio files are central to the app. They are recordings of people on Guernsey speaking Guernesiais, and sizes range from 1.6Mb to 2.6Mb.

In iOS a player is created with mobileControlCreate, and the audio controller is visible, so the user can pause, fast fwd etc. 

The app design and coding is done and it works perfectly in the IDE, as Mac standalone (with standard player) and in the iOS simulator (iOS 13.3). 

It works on the client’s iPads too (iOS 13.6), but irregularly freezes (rarely crashes), preventing further interaction until the app is killed and restarted. The freeze occurs at (or during)  
”mobileControlSet "voicePlayer", "filename", sAudioPath”

In the simulator I get a crash (app quits) if I don’t put ”wait 20 ticks with messages” after setting the file path, but never a freeze. I’ve tried to give the audio loading a full second wait, in case iPads are slower than simulator, and it prevents crash but not the random freezing.

The iPad user can sometimes load the same profile (or different ones, we see no pattern) 30-40 times before freeze occurs, sometimes just 3. So it doesn’t seem to have anything to do with cache build-up or so. 

So, has anyone experienced similar problems with playing mp3 files on iOS?
Any obvious pitfalls? 

The frustrating thing is that I cannot reproduce the problem in simulator (it works perfectly there), and have no iPad myself to hook up for Remote debugging. So I have to try various solutions, then upload a new build to TestFlight and wait for the client’s ”Sorry, it’s still freezing randomly”…

Help!

Hopeful greetings,
Andreas 
WhenInSpace