Running four different apps which use Siri shortcuts, my app claims there are no existing voice shortcuts created. INVoiceShortcutCenter's getAllVoiceShortcutsWithCompletion completes without an error, but the callback is always passed an empty array of INVoiceShortcuts.
If I try and add a new shortcut using my suggested phrase I receive an alert "Name Cannot Be Used" with the message "You already have a shortcut named '...'. Please choose another name for this shortcut".
If I choose another phrase and add a voice shortcut for that it is added, but getAllVoiceShortcutsWithCompletion still returns no shortcuts. Both the existing (created on iOS 12) and the newly-added voice shortcut appear in the Apple Shortcuts app and seem to function correctly.
A Stack Overflow question created on July 4th 2019 reports the same issue: https://stackoverflow.com/questions/56884855/invoiceshortcutcenter-shared-getallvoiceshortcuts-does-not-return-anything-in-io
The Xcode 11 build run on iOS 12 works as expected.
The App Store version (built with Xcode 10) run on iOS 13 beta 4 seems to fail the availability check in the code for iOS 12 so doesn't even show me the UI to access the Siri shortcuts section of my app! That's a whole separate issue...