Faced with the same issue. Tried everything. My steps: Verify that your app and your app's extension have the same signing certificate in Release, Debug and AD-hoc signing. Set Bundle identifier to every target (main app and extension) manually to .plist When building on real device try to increase build version for the main app and target app. I don't know how signing works, but that solved my problem.

Thanks for the answer! I am using UICollectionView.CellRegistration<UICollectionViewListCell, Item>. So seems like I need to inherit from UICollectionViewListCell with code from documentation.