The SpringBoard (more commonly known as the Home Screen), is the standard application that manages the iOS home screen.
I made an example .mfa which includes my background atmosphere sample (under water bubbles) on an infinite loop. This is an .ogg file, but I've also tried with mp3s and wavs and the same problem occurs. Please try exporting it to Xcode and installing it on an iOS device. You'll see a blank white screen, but you should hear the under water bubbling sound FX loop. Then minimise the app to the home screen and switch back to it. The sound sample doesn't resume playing.
Well I just tried uploading the .mfa but it wouldn't upload. Then I found the maximum file size allowed for an .mfa is 1MB, but the minimum file size of an iOS .mfa seems to be 4.3MB, even if it is totally void of code or data elements.
Anyway, all I have in the event editor is:
Start of Frame - Play sample Under Water Bubbles (uninterruptible) 0 times
Please could you try this with any sound sample?