Assertion failed: "Attempted to load bulk data from an invalid filename" on iOS

There is a runtime crash on iOS a second into launching the app, right at the UE splash screen. Following are a few messages from the phone logs – it appears the engine is not able to read some asset files for reasons unknown and the failed assertion is causing the crash (BulkData.cpp:1864 has a checkf against the FileName), but I’ve yet to figure out why the engine is not finding the relevant assets.

    [UE4] Assertion failed: Ar != __null [File:/Users/build/Build/++UE4/Sync/Engine/Source/Runtime/CoreUObject/Private/Serialization/BulkData.cpp] [Line: 1864]
    Attempted to load bulk data from an invalid filename '../../../XXX/Content/Audio/Waves/WAVE_hard_thump_01.m.ubulk

It turns out even though the option to generate “ubulk” files is true by default and the engine should not look for them if it is not creating them, UE was looking for “ubulk” files but not generating them. Adding the following lines to DefaultEngine.ini fixed the issue.