They're just very slow, and at least until iOS 10, apps that were in the "restoring" state displayed no indication of such. I was told by an Apple retail employ

They're just very slow, and at least until iOS 10, apps that were in the "restoring" state displayed no indication of such. I was told by an Apple retail employee that in most cases WhatsApp was always the last app to finish restoring, which was exactly the app that was "stuck" for me. I assume it is because the iPhone is decrypting the backup, but it's just that it is doing it very slowly for some reason.