In order to support AudioUnit (AU) we had to use a different form of storage (AppGroup).
User files cannot be retrieved with iTunes, please use export solutions instead (see the two following questions How can I import my own samples from iCloud Drive, Dropbox, Google Drive or OneDrive? and How can I import my own samples from iCloud Drive, Dropbox, Google Drive or OneDrive?).
However, you can add files into BeatHawk using iTunes, they will be moved to the right folder during app startup.