UIDocumentPickerViewController not loading document from iCloud on device - icloud

Question

I just tried to add iOS's document picker (UIDocumentPickerViewController) as directed by the Document Picker Programming Guide
I'm trying to Import (i.e. copy locally...hopefully the simplest case) a file using the iCloud document provider (I've tested others such as DropBox and Google Drive and they work fine). Here's how I call up the document picker menu:
...
UIDocumentMenuViewController *documentPickerMenu = [[UIDocumentMenuViewController alloc]
initWithDocumentTypes:#[#"public.text", #"public.data"]
inMode:UIDocumentPickerModeImport];
documentPickerMenu.delegate = self;
[self presentViewController:documentPickerMenu animated:YES completion:nil];
...
and here is how I bring up the provider-specific document picker:
- (void)documentMenu:(UIDocumentMenuViewController *)documentMenu didPickDocumentPicker:(UIDocumentPickerViewController *)documentPicker
{
documentPicker.delegate = self;
[self presentViewController:documentPicker animated:YES completion:nil];
}
and here is my delegate function, which never gets called (i.e. never see log line, breakpoint never hit):
- (void)documentPicker:(UIDocumentPickerViewController *)controller didPickDocumentAtURL:(NSURL *)url {
if (controller.documentPickerMode == UIDocumentPickerModeImport) {
NSLog(#"Opened %#", url.path);
}
}
I tested it and it worked fine on the iOS simulator. However when I load it on an iOS device (an iPad), the document picker comes up fine, shows me valid iCloud documents, but when I pick one all I see in the console is:
plugin com.apple.UIKit.fileprovider.default invalidated
And my delegate function UIDocumentPickerDelegate:didPickDocumentAtURL: function is never called.
I believe I have properly provisioned the application with the iCloud entitlements.
Can someone please help?