iCloud UIDocumentPicker crashes intermittently and hangs

Question

Issue:

When choosing a document from iCloud the application randomly crashes, for most of the time the following code will work, but on rare occasions it will fail.

Answer 1

I recently stumpled opon the same problem:

*** Assertion failure in -[UIDocumentPickerViewController _commonInitWithCompletion:]

is caused due to lacking App-Capabilities. Go to your Build and choose Capabilities -> iCloud

Activate it via the switch on the right hand side and toggle iCloud Documents and CloudKit ON. (Notice: This will only work with a payed developer account)

Rebuild->Run

Also have in mind:

iCloud entitlements are available only to apps submitted to the App Store or to the Mac App Store. (Source)