I have an app, that requires authorisation in the settings to fetch data. If after installation the user opens the settings first and then authorises the service, the resulting data is never sent to the device.
It appears the App must first be opened before the file can be found using the inbox.nextFile.
The file transfer works when using the developer bridge because the app is opened automatically as part of the build and deploy process. Once you are using the GAM link, there is nothing forcing the app to be opened first.
I can reproduce this bug.