Have you investigated JUCE_IOS_AUDIO_EXPLICIT_SAMPLERATES at all? There’s some more info in this thread:
Essentially, there doesn’t seem to be an API for an interface to advertise its supported rates on iOS. Instead, the app has to query the rates that it wants to use. By setting JUCE_IOS_AUDIO_EXPLICIT_SAMPLERATES, you can limit the number of different samle rates that are tested.
The crash seems like a problem that would be good to fix, but it’s likely to be difficult to repro without hardware that causes the problem. Have you tested any other devices, and if so, do they behave in the same way?