UIDocumentPickerController access denied Cocoa Error 257 - ios

Question

I'm trying to import a custom file from one of my apps to another one (let's call them App_A and App_B). If I export the file directly from App_A and in the share sheet I select App_B everything works fine.
My problem is that the file is saved in iCloud Drive so the user can access it through the system's File app. When I try to select the same file from Files app or in App_B through UIDocumentPickerViewController.
In both cases I run the following code (inside UIDocumentPickerDelegate or AppDelegate):
let access = url.startAccessingSecurityScopedResource()
var error: NSError? = nil
NSFileCoordinator().coordinate(readingItemAt: url, error: &error) { (coorURL) in
do{
let data = try Data(contentsOf: coorURL)
}catch{
print("manage error: \(error.localizedDescription)")
}
if access{
url.stopAccessingSecurityScopedResource()
}
}
The error I get is always the same:
Error Domain=NSCocoaErrorDomain Code=257 ... NSUnderlyingError=0x2803e07b0 {Error Domain=NSPOSIXErrorDomain Code=13 "Permission denied"}} and url.startAccessingSecurityScopedResource() returns always false.
I'm doing this on Xcode 11.4.1, Swift 5, iOS 13.3.1 on device and 13.4.1 on simulator, but the result doesn't change.
Do you have an idea about this weird error? I suppose that if the user select a file and an app to open it the permission would be granted, but probably I'm missing something. Could you help?