I just restored my iPhone from iTunes. At backup time a Bitcoin app was installed on iPhone, with an already created wallet with a balance. After restore, Copay in on iPhone, but when starting the wallet balance is not included in the app. Why?
Wallets and apps that store sensitive data usually store passwords/encryption keys in keychain. If the backup was not encrypted, unfortunately, only app developers may be able to help.
Also, some banking apps and wallets don't include this data in the backup and have another way of transferring accounts or passwords.
p.s. @Steve Chambers is right, you should always have an encrypted backup, even with an easy password like '12345', just to back up as mutch data as possible.